<?xml version="1.0" encoding="windows-1252"?>
<!--XBRL document created with Rivet Software Powered by Crossfire 5.9.110.0 -->
<!--Based on XBRL 2.1-->
<!--Created on: 4/25/2014 3:59:58 PM-->
<!--Modified on: 4/25/2014 3:59:58 PM-->
<linkbase xmlns="http://www.xbrl.org/2003/linkbase" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:xbrldt="http://xbrl.org/2005/xbrldt" xsi:schemaLocation="http://www.xbrl.org/2003/linkbase http://www.xbrl.org/2003/xbrl-linkbase-2003-12-31.xsd">
  <roleRef xlink:type="simple" xlink:href="idxx-20140331.xsd#DisclosureDerivativeInstrumentsAndHedgingTables" roleURI="http://www.idexx.com/role/DisclosureDerivativeInstrumentsAndHedgingTables"/>
  <roleRef xlink:type="simple" xlink:href="idxx-20140331.xsd#DisclosureAccumulatedOtherComprehensiveIncomeScheduleOfReclassificationsOutOfAccumulatedOtherComprehensiveIncomeDetails" roleURI="http://www.idexx.com/role/DisclosureAccumulatedOtherComprehensiveIncomeScheduleOfReclassificationsOutOfAccumulatedOtherComprehensiveIncomeDetails"/>
  <roleRef xlink:type="simple" xlink:href="idxx-20140331.xsd#DisclosureEarningsPerShareScheduleOfNumberOfAntiDilutiveStockOptionsAndRestrictedStockUnitsDetails" roleURI="http://www.idexx.com/role/DisclosureEarningsPerShareScheduleOfNumberOfAntiDilutiveStockOptionsAndRestrictedStockUnitsDetails"/>
  <roleRef xlink:type="simple" xlink:href="idxx-20140331.xsd#DisclosureSegmentReportingSummaryOfSegmentPerformanceDetails" roleURI="http://www.idexx.com/role/DisclosureSegmentReportingSummaryOfSegmentPerformanceDetails"/>
  <roleRef xlink:type="simple" xlink:href="idxx-20140331.xsd#DisclosureSegmentReportingSummaryOfRevenueByProductAndServiceCategoryDetails" roleURI="http://www.idexx.com/role/DisclosureSegmentReportingSummaryOfRevenueByProductAndServiceCategoryDetails"/>
  <roleRef xlink:type="simple" xlink:href="idxx-20140331.xsd#DisclosureFairValueMeasurementsScheduleOfFairValueOfAssetsAndLiabilitiesMeasuredOnRecurringBasisDetails" roleURI="http://www.idexx.com/role/DisclosureFairValueMeasurementsScheduleOfFairValueOfAssetsAndLiabilitiesMeasuredOnRecurringBasisDetails"/>
  <roleRef xlink:type="simple" xlink:href="idxx-20140331.xsd#DisclosureDerivativeInstrumentsAndHedgingNarrativeDetails" roleURI="http://www.idexx.com/role/DisclosureDerivativeInstrumentsAndHedgingNarrativeDetails"/>
  <roleRef xlink:type="simple" xlink:href="idxx-20140331.xsd#DisclosureDerivativeInstrumentsAndHedgingScheduleOfFairValuesAndBalanceSheetClassificationsOfDerivativesDesignatedAsHedgingInstrumentsDetails" roleURI="http://www.idexx.com/role/DisclosureDerivativeInstrumentsAndHedgingScheduleOfFairValuesAndBalanceSheetClassificationsOfDerivativesDesignatedAsHedgingInstrumentsDetails"/>
  <roleRef xlink:type="simple" xlink:href="idxx-20140331.xsd#DisclosureDerivativeInstrumentsAndHedgingGainLossRecognizedInOtherComprehensiveIncomeOnDerivativeInstrumentsEffectivePortionDetails" roleURI="http://www.idexx.com/role/DisclosureDerivativeInstrumentsAndHedgingGainLossRecognizedInOtherComprehensiveIncomeOnDerivativeInstrumentsEffectivePortionDetails"/>
  <arcroleRef xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#hypercube-dimension" arcroleURI="http://xbrl.org/int/dim/arcrole/hypercube-dimension"/>
  <arcroleRef xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-domain" arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-domain"/>
  <arcroleRef xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-default" arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-default"/>
  <arcroleRef xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#all" arcroleURI="http://xbrl.org/int/dim/arcrole/all"/>
  <arcroleRef xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#domain-member" arcroleURI="http://xbrl.org/int/dim/arcrole/domain-member"/>
  <definitionLink xlink:role="http://www.idexx.com/role/DisclosureDerivativeInstrumentsAndHedgingTables" xlink:type="extended" xlink:title="31503 - Disclosure - Derivative Instruments And Hedging (Tables)">
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsTable" xlink:label="us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsTable"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_DerivativeInstrumentRiskAxis" xlink:label="us-gaap_DerivativeInstrumentRiskAxis"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="1" xlink:from="us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsTable" xlink:to="us-gaap_DerivativeInstrumentRiskAxis" use="optional"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_DerivativeContractTypeDomain" xlink:label="us-gaap_DerivativeContractTypeDomain"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_DerivativeInstrumentRiskAxis" xlink:to="us-gaap_DerivativeContractTypeDomain" use="optional"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_DerivativeContractTypeDomain" xlink:label="us-gaap_DerivativeContractTypeDomain_635340383948735773"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" order="1" xlink:from="us-gaap_DerivativeInstrumentRiskAxis" xlink:to="us-gaap_DerivativeContractTypeDomain_635340383948735773" use="optional"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_DerivativeFinancialInstrumentsAssetsMember" xlink:label="us-gaap_DerivativeFinancialInstrumentsAssetsMember"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_DerivativeContractTypeDomain" xlink:to="us-gaap_DerivativeFinancialInstrumentsAssetsMember" use="optional"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_DerivativeFinancialInstrumentsLiabilitiesMember" xlink:label="us-gaap_DerivativeFinancialInstrumentsLiabilitiesMember"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_DerivativeContractTypeDomain" xlink:to="us-gaap_DerivativeFinancialInstrumentsLiabilitiesMember" use="optional"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_DerivativeLineItems" xlink:label="us-gaap_DerivativeLineItems"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" order="1" xlink:from="us-gaap_DerivativeLineItems" xlink:to="us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsTable" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ScheduleOfDerivativeInstrumentsInStatementOfFinancialPositionFairValueTextBlock" xlink:label="us-gaap_ScheduleOfDerivativeInstrumentsInStatementOfFinancialPositionFairValueTextBlock"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_DerivativeLineItems" xlink:to="us-gaap_ScheduleOfDerivativeInstrumentsInStatementOfFinancialPositionFairValueTextBlock" priority="1" use="optional"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ScheduleOfDerivativeInstrumentsEffectOnOtherComprehensiveIncomeLossTableTextBlock" xlink:label="us-gaap_ScheduleOfDerivativeInstrumentsEffectOnOtherComprehensiveIncomeLossTableTextBlock"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_DerivativeLineItems" xlink:to="us-gaap_ScheduleOfDerivativeInstrumentsEffectOnOtherComprehensiveIncomeLossTableTextBlock" priority="1" use="optional"/>
  </definitionLink>
  <definitionLink xlink:role="http://www.idexx.com/role/DisclosureAccumulatedOtherComprehensiveIncomeScheduleOfReclassificationsOutOfAccumulatedOtherComprehensiveIncomeDetails" xlink:type="extended" xlink:title="41002 - Disclosure - Accumulated Other Comprehensive Income (Schedule of Reclassifications out of Accumulated Other Comprehensive Income) (Details)">
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_StatementTable" xlink:label="us-gaap_StatementTable"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_OtherComprehensiveIncomeLocationAxis" xlink:label="us-gaap_OtherComprehensiveIncomeLocationAxis"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="1" xlink:from="us-gaap_StatementTable" xlink:to="us-gaap_OtherComprehensiveIncomeLocationAxis" use="optional"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_OtherComprehensiveIncomeLocationDomain" xlink:label="us-gaap_OtherComprehensiveIncomeLocationDomain"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_OtherComprehensiveIncomeLocationAxis" xlink:to="us-gaap_OtherComprehensiveIncomeLocationDomain" use="optional"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_OtherComprehensiveIncomeLocationDomain" xlink:label="us-gaap_OtherComprehensiveIncomeLocationDomain_635340383948735773"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" order="1" xlink:from="us-gaap_OtherComprehensiveIncomeLocationAxis" xlink:to="us-gaap_OtherComprehensiveIncomeLocationDomain_635340383948735773" use="optional"/>
    <loc xlink:type="locator" xlink:href="idxx-20140331.xsd#idxx_InterestRateSwapsMember" xlink:label="idxx_InterestRateSwapsMember"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_OtherComprehensiveIncomeLocationDomain" xlink:to="idxx_InterestRateSwapsMember" priority="1" use="optional"/>
    <loc xlink:type="locator" xlink:href="idxx-20140331.xsd#idxx_ForeignCurrencyExchangeContractsMember" xlink:label="idxx_ForeignCurrencyExchangeContractsMember"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_OtherComprehensiveIncomeLocationDomain" xlink:to="idxx_ForeignCurrencyExchangeContractsMember" priority="1" use="optional"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_IncomeStatementLocationAxis" xlink:label="us-gaap_IncomeStatementLocationAxis"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="2" xlink:from="us-gaap_StatementTable" xlink:to="us-gaap_IncomeStatementLocationAxis" use="optional"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_IncomeStatementLocationDomain" xlink:label="us-gaap_IncomeStatementLocationDomain"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_IncomeStatementLocationAxis" xlink:to="us-gaap_IncomeStatementLocationDomain" use="optional"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_IncomeStatementLocationDomain" xlink:label="us-gaap_IncomeStatementLocationDomain_635340383948735773"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" order="1" xlink:from="us-gaap_IncomeStatementLocationAxis" xlink:to="us-gaap_IncomeStatementLocationDomain_635340383948735773" use="optional"/>
    <loc xlink:type="locator" xlink:href="idxx-20140331.xsd#idxx_ReclassificationsOutOfAccumulatedOtherComprehensiveIncomeMember" xlink:label="idxx_ReclassificationsOutOfAccumulatedOtherComprehensiveIncomeMember"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_IncomeStatementLocationDomain" xlink:to="idxx_ReclassificationsOutOfAccumulatedOtherComprehensiveIncomeMember" priority="1" use="optional"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_StatementLineItems" xlink:label="us-gaap_StatementLineItems"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" order="1" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_StatementTable" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodBeforeTax" xlink:label="us-gaap_ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodBeforeTax"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodBeforeTax" priority="1" use="optional"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodNetOfTax" xlink:label="us-gaap_ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodNetOfTax"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodNetOfTax" priority="1" use="optional"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_IncomeTaxExpenseBenefit" xlink:label="us-gaap_IncomeTaxExpenseBenefit"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_IncomeTaxExpenseBenefit" priority="1" use="optional"/>
  </definitionLink>
  <definitionLink xlink:role="http://www.idexx.com/role/DisclosureEarningsPerShareScheduleOfNumberOfAntiDilutiveStockOptionsAndRestrictedStockUnitsDetails" xlink:type="extended" xlink:title="41102 - Disclosure - Earnings Per Share (Schedule Of Number Of Anti-Dilutive Stock Options and Restricted Stock Units) (Details)">
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable" xlink:label="us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis" xlink:label="us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="1" xlink:from="us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable" xlink:to="us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis" use="optional"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_AntidilutiveSecuritiesNameDomain" xlink:label="us-gaap_AntidilutiveSecuritiesNameDomain"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis" xlink:to="us-gaap_AntidilutiveSecuritiesNameDomain" use="optional"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_AntidilutiveSecuritiesNameDomain" xlink:label="us-gaap_AntidilutiveSecuritiesNameDomain_635340383948735773"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" order="1" xlink:from="us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis" xlink:to="us-gaap_AntidilutiveSecuritiesNameDomain_635340383948735773" use="optional"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_EmployeeStockOptionMember" xlink:label="us-gaap_EmployeeStockOptionMember"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_AntidilutiveSecuritiesNameDomain" xlink:to="us-gaap_EmployeeStockOptionMember" use="optional"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_RestrictedStockUnitsRSUMember" xlink:label="us-gaap_RestrictedStockUnitsRSUMember"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_AntidilutiveSecuritiesNameDomain" xlink:to="us-gaap_RestrictedStockUnitsRSUMember" use="optional"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems" xlink:label="us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" order="1" xlink:from="us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems" xlink:to="us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount" xlink:label="us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems" xlink:to="us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount" priority="1" use="optional"/>
  </definitionLink>
  <definitionLink xlink:role="http://www.idexx.com/role/DisclosureSegmentReportingSummaryOfSegmentPerformanceDetails" xlink:type="extended" xlink:title="41301 - Disclosure - Segment Reporting (Summary Of Segment Performance) (Details)">
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable" xlink:label="us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_StatementBusinessSegmentsAxis" xlink:label="us-gaap_StatementBusinessSegmentsAxis"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="1" xlink:from="us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable" xlink:to="us-gaap_StatementBusinessSegmentsAxis" use="optional"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_SegmentDomain" xlink:label="us-gaap_SegmentDomain"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_StatementBusinessSegmentsAxis" xlink:to="us-gaap_SegmentDomain" use="optional"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_SegmentDomain" xlink:label="us-gaap_SegmentDomain_635340383948891774"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" order="1" xlink:from="us-gaap_StatementBusinessSegmentsAxis" xlink:to="us-gaap_SegmentDomain_635340383948891774" use="optional"/>
    <loc xlink:type="locator" xlink:href="idxx-20140331.xsd#idxx_CagSegmentMember" xlink:label="idxx_CagSegmentMember"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_SegmentDomain" xlink:to="idxx_CagSegmentMember" priority="1" use="optional"/>
    <loc xlink:type="locator" xlink:href="idxx-20140331.xsd#idxx_WaterSegmentMember" xlink:label="idxx_WaterSegmentMember"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_SegmentDomain" xlink:to="idxx_WaterSegmentMember" priority="1" use="optional"/>
    <loc xlink:type="locator" xlink:href="idxx-20140331.xsd#idxx_LpdSegmentMember" xlink:label="idxx_LpdSegmentMember"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_SegmentDomain" xlink:to="idxx_LpdSegmentMember" priority="1" use="optional"/>
    <loc xlink:type="locator" xlink:href="idxx-20140331.xsd#idxx_OtherSegmentMember" xlink:label="idxx_OtherSegmentMember"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_SegmentDomain" xlink:to="idxx_OtherSegmentMember" priority="1" use="optional"/>
    <loc xlink:type="locator" xlink:href="idxx-20140331.xsd#idxx_UnallocatedAmountsMember" xlink:label="idxx_UnallocatedAmountsMember"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="us-gaap_SegmentDomain" xlink:to="idxx_UnallocatedAmountsMember" priority="1" use="optional"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_SegmentReportingInformationLineItems" xlink:label="us-gaap_SegmentReportingInformationLineItems"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" order="1" xlink:from="us-gaap_SegmentReportingInformationLineItems" xlink:to="us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_SalesRevenueNet" xlink:label="us-gaap_SalesRevenueNet"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_SegmentReportingInformationLineItems" xlink:to="us-gaap_SalesRevenueNet" priority="1" use="optional"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_OperatingIncomeLoss" xlink:label="us-gaap_OperatingIncomeLoss"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_SegmentReportingInformationLineItems" xlink:to="us-gaap_OperatingIncomeLoss" priority="1" use="optional"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_InterestIncomeExpenseNonoperatingNet" xlink:label="us-gaap_InterestIncomeExpenseNonoperatingNet"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_SegmentReportingInformationLineItems" xlink:to="us-gaap_InterestIncomeExpenseNonoperatingNet" priority="1" use="optional"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments" xlink:label="us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="us-gaap_SegmentReportingInformationLineItems" xlink:to="us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments" priority="1" use="optional"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_IncomeTaxExpenseBenefit" xlink:label="us-gaap_IncomeTaxExpenseBenefit"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="6" xlink:from="us-gaap_SegmentReportingInformationLineItems" xlink:to="us-gaap_IncomeTaxExpenseBenefit" priority="1" use="optional"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ProfitLoss" xlink:label="us-gaap_ProfitLoss"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="7" xlink:from="us-gaap_SegmentReportingInformationLineItems" xlink:to="us-gaap_ProfitLoss" priority="1" use="optional"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_NetIncomeLossAttributableToNoncontrollingInterest" xlink:label="us-gaap_NetIncomeLossAttributableToNoncontrollingInterest"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="8" xlink:from="us-gaap_SegmentReportingInformationLineItems" xlink:to="us-gaap_NetIncomeLossAttributableToNoncontrollingInterest" priority="1" use="optional"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_NetIncomeLoss" xlink:label="us-gaap_NetIncomeLoss"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="9" xlink:from="us-gaap_SegmentReportingInformationLineItems" xlink:to="us-gaap_NetIncomeLoss" priority="1" use="optional"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_DepreciationDepletionAndAmortization" xlink:label="us-gaap_DepreciationDepletionAndAmortization"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="10" xlink:from="us-gaap_SegmentReportingInformationLineItems" xlink:to="us-gaap_DepreciationDepletionAndAmortization" priority="1" use="optional"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_PaymentsToAcquirePropertyPlantAndEquipment" xlink:label="us-gaap_PaymentsToAcquirePropertyPlantAndEquipment"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="11" xlink:from="us-gaap_SegmentReportingInformationLineItems" xlink:to="us-gaap_PaymentsToAcquirePropertyPlantAndEquipment" priority="1" use="optional"/>
  </definitionLink>
  <definitionLink xlink:role="http://www.idexx.com/role/DisclosureSegmentReportingSummaryOfRevenueByProductAndServiceCategoryDetails" xlink:type="extended" xlink:title="41302 - Disclosure - Segment Reporting (Summary Of Revenue By Product And Service Category) (Details)">
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable" xlink:label="us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_StatementBusinessSegmentsAxis" xlink:label="us-gaap_StatementBusinessSegmentsAxis"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="1" xlink:from="us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable" xlink:to="us-gaap_StatementBusinessSegmentsAxis" use="optional"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_SegmentDomain" xlink:label="us-gaap_SegmentDomain"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_StatementBusinessSegmentsAxis" xlink:to="us-gaap_SegmentDomain" use="optional"/>
    <loc xlink:type="locator" xlink:href="idxx-20140331.xsd#idxx_CagSegmentMember" xlink:label="idxx_CagSegmentMember"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_SegmentDomain" xlink:to="idxx_CagSegmentMember" priority="1" use="optional"/>
    <loc xlink:type="locator" xlink:href="idxx-20140331.xsd#idxx_WaterSegmentMember" xlink:label="idxx_WaterSegmentMember"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_SegmentDomain" xlink:to="idxx_WaterSegmentMember" priority="1" use="optional"/>
    <loc xlink:type="locator" xlink:href="idxx-20140331.xsd#idxx_LpdSegmentMember" xlink:label="idxx_LpdSegmentMember"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_SegmentDomain" xlink:to="idxx_LpdSegmentMember" priority="1" use="optional"/>
    <loc xlink:type="locator" xlink:href="idxx-20140331.xsd#idxx_OtherSegmentMember" xlink:label="idxx_OtherSegmentMember"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_SegmentDomain" xlink:to="idxx_OtherSegmentMember" priority="1" use="optional"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ProductOrServiceAxis" xlink:label="us-gaap_ProductOrServiceAxis"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="2" xlink:from="us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable" xlink:to="us-gaap_ProductOrServiceAxis" use="optional"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ProductsAndServicesDomain" xlink:label="us-gaap_ProductsAndServicesDomain"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_ProductOrServiceAxis" xlink:to="us-gaap_ProductsAndServicesDomain" use="optional"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ProductsAndServicesDomain" xlink:label="us-gaap_ProductsAndServicesDomain_635340383948891774"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" order="1" xlink:from="us-gaap_ProductOrServiceAxis" xlink:to="us-gaap_ProductsAndServicesDomain_635340383948891774" use="optional"/>
    <loc xlink:type="locator" xlink:href="idxx-20140331.xsd#idxx_CagDiagnosticsRecurringRevenueMember" xlink:label="idxx_CagDiagnosticsRecurringRevenueMember"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_ProductsAndServicesDomain" xlink:to="idxx_CagDiagnosticsRecurringRevenueMember" priority="1" use="optional"/>
    <loc xlink:type="locator" xlink:href="idxx-20140331.xsd#idxx_IdexxVetlabConsumablesMember" xlink:label="idxx_IdexxVetlabConsumablesMember"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_ProductsAndServicesDomain" xlink:to="idxx_IdexxVetlabConsumablesMember" priority="1" use="optional"/>
    <loc xlink:type="locator" xlink:href="idxx-20140331.xsd#idxx_VetlabServiceAndAccessoriesMember" xlink:label="idxx_VetlabServiceAndAccessoriesMember"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_ProductsAndServicesDomain" xlink:to="idxx_VetlabServiceAndAccessoriesMember" priority="1" use="optional"/>
    <loc xlink:type="locator" xlink:href="idxx-20140331.xsd#idxx_RapidAssayProductsMember" xlink:label="idxx_RapidAssayProductsMember"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_ProductsAndServicesDomain" xlink:to="idxx_RapidAssayProductsMember" priority="1" use="optional"/>
    <loc xlink:type="locator" xlink:href="idxx-20140331.xsd#idxx_ReferenceLaboratoryDiagnosticAndConsultingServicesMember" xlink:label="idxx_ReferenceLaboratoryDiagnosticAndConsultingServicesMember"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="us-gaap_ProductsAndServicesDomain" xlink:to="idxx_ReferenceLaboratoryDiagnosticAndConsultingServicesMember" priority="1" use="optional"/>
    <loc xlink:type="locator" xlink:href="idxx-20140331.xsd#idxx_CagDiagnosticCaptailVetlabInstrumentsMember" xlink:label="idxx_CagDiagnosticCaptailVetlabInstrumentsMember"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="6" xlink:from="us-gaap_ProductsAndServicesDomain" xlink:to="idxx_CagDiagnosticCaptailVetlabInstrumentsMember" priority="1" use="optional"/>
    <loc xlink:type="locator" xlink:href="idxx-20140331.xsd#idxx_CustomerInformationManagmentAndDigitalImagingSystemsMember" xlink:label="idxx_CustomerInformationManagmentAndDigitalImagingSystemsMember"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="7" xlink:from="us-gaap_ProductsAndServicesDomain" xlink:to="idxx_CustomerInformationManagmentAndDigitalImagingSystemsMember" priority="1" use="optional"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_SegmentReportingInformationLineItems" xlink:label="us-gaap_SegmentReportingInformationLineItems"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" order="1" xlink:from="us-gaap_SegmentReportingInformationLineItems" xlink:to="us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_SalesRevenueNet" xlink:label="us-gaap_SalesRevenueNet"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_SegmentReportingInformationLineItems" xlink:to="us-gaap_SalesRevenueNet" priority="1" use="optional"/>
  </definitionLink>
  <definitionLink xlink:role="http://www.idexx.com/role/DisclosureFairValueMeasurementsScheduleOfFairValueOfAssetsAndLiabilitiesMeasuredOnRecurringBasisDetails" xlink:type="extended" xlink:title="41401 - Disclosure - Fair Value Measurements (Schedule Of Fair Value Of Assets And Liabilities Measured On Recurring Basis) (Details)">
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable" xlink:label="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_FairValueByMeasurementFrequencyAxis" xlink:label="us-gaap_FairValueByMeasurementFrequencyAxis"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="1" xlink:from="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable" xlink:to="us-gaap_FairValueByMeasurementFrequencyAxis" use="optional"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_FairValueMeasurementFrequencyDomain" xlink:label="us-gaap_FairValueMeasurementFrequencyDomain"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_FairValueByMeasurementFrequencyAxis" xlink:to="us-gaap_FairValueMeasurementFrequencyDomain" use="optional"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_FairValueMeasurementFrequencyDomain" xlink:label="us-gaap_FairValueMeasurementFrequencyDomain_635340383948891774"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" order="1" xlink:from="us-gaap_FairValueByMeasurementFrequencyAxis" xlink:to="us-gaap_FairValueMeasurementFrequencyDomain_635340383948891774" use="optional"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_FairValueMeasurementsRecurringMember" xlink:label="us-gaap_FairValueMeasurementsRecurringMember"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_FairValueMeasurementFrequencyDomain" xlink:to="us-gaap_FairValueMeasurementsRecurringMember" use="optional"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_DerivativeInstrumentRiskAxis" xlink:label="us-gaap_DerivativeInstrumentRiskAxis"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="2" xlink:from="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable" xlink:to="us-gaap_DerivativeInstrumentRiskAxis" use="optional"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_DerivativeContractTypeDomain" xlink:label="us-gaap_DerivativeContractTypeDomain"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_DerivativeInstrumentRiskAxis" xlink:to="us-gaap_DerivativeContractTypeDomain" use="optional"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_MoneyMarketFundsMember" xlink:label="us-gaap_MoneyMarketFundsMember"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_DerivativeContractTypeDomain" xlink:to="us-gaap_MoneyMarketFundsMember" use="optional"/>
    <loc xlink:type="locator" xlink:href="idxx-20140331.xsd#idxx_EquityMutualFundsMember" xlink:label="idxx_EquityMutualFundsMember"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_DerivativeContractTypeDomain" xlink:to="idxx_EquityMutualFundsMember" priority="1" use="optional"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ForeignExchangeContractMember" xlink:label="us-gaap_ForeignExchangeContractMember"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_DerivativeContractTypeDomain" xlink:to="us-gaap_ForeignExchangeContractMember" use="optional"/>
    <loc xlink:type="locator" xlink:href="idxx-20140331.xsd#idxx_DeferredCompensationMember" xlink:label="idxx_DeferredCompensationMember"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_DerivativeContractTypeDomain" xlink:to="idxx_DeferredCompensationMember" priority="1" use="optional"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_InterestRateSwapMember" xlink:label="us-gaap_InterestRateSwapMember"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="us-gaap_DerivativeContractTypeDomain" xlink:to="us-gaap_InterestRateSwapMember" use="optional"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis" xlink:label="us-gaap_FairValueByFairValueHierarchyLevelAxis"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="3" xlink:from="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable" xlink:to="us-gaap_FairValueByFairValueHierarchyLevelAxis" use="optional"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:label="us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_FairValueByFairValueHierarchyLevelAxis" xlink:to="us-gaap_FairValueMeasurementsFairValueHierarchyDomain" use="optional"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:label="us-gaap_FairValueMeasurementsFairValueHierarchyDomain_635340383948891774"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" order="1" xlink:from="us-gaap_FairValueByFairValueHierarchyLevelAxis" xlink:to="us-gaap_FairValueMeasurementsFairValueHierarchyDomain_635340383948891774" use="optional"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_FairValueInputsLevel1Member" xlink:label="us-gaap_FairValueInputsLevel1Member"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:to="us-gaap_FairValueInputsLevel1Member" use="optional"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_FairValueInputsLevel2Member" xlink:label="us-gaap_FairValueInputsLevel2Member"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:to="us-gaap_FairValueInputsLevel2Member" use="optional"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems" xlink:label="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" order="1" xlink:from="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems" xlink:to="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_PrepaidExpenseAndOtherAssetsAbstract" xlink:label="us-gaap_PrepaidExpenseAndOtherAssetsAbstract"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems" xlink:to="us-gaap_PrepaidExpenseAndOtherAssetsAbstract" priority="1" use="optional"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_NotesReceivableRelatedPartiesNoncurrent" xlink:label="us-gaap_NotesReceivableRelatedPartiesNoncurrent"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_PrepaidExpenseAndOtherAssetsAbstract" xlink:to="us-gaap_NotesReceivableRelatedPartiesNoncurrent" priority="1" use="optional"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_AssetsFairValueDisclosure" xlink:label="us-gaap_AssetsFairValueDisclosure"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems" xlink:to="us-gaap_AssetsFairValueDisclosure" priority="1" use="optional"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_LiabilitiesFairValueDisclosure" xlink:label="us-gaap_LiabilitiesFairValueDisclosure"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems" xlink:to="us-gaap_LiabilitiesFairValueDisclosure" priority="1" use="optional"/>
  </definitionLink>
  <definitionLink xlink:role="http://www.idexx.com/role/DisclosureDerivativeInstrumentsAndHedgingNarrativeDetails" xlink:type="extended" xlink:title="41501 - Disclosure - Derivative Instruments And Hedging (Narrative) (Details)">
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_LineOfCreditFacilityTable" xlink:label="us-gaap_LineOfCreditFacilityTable"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_LineOfCreditFacilityAxis" xlink:label="us-gaap_LineOfCreditFacilityAxis"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="1" xlink:from="us-gaap_LineOfCreditFacilityTable" xlink:to="us-gaap_LineOfCreditFacilityAxis" use="optional"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_LineOfCreditFacilityLenderDomain" xlink:label="us-gaap_LineOfCreditFacilityLenderDomain"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_LineOfCreditFacilityAxis" xlink:to="us-gaap_LineOfCreditFacilityLenderDomain" use="optional"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_LineOfCreditFacilityLenderDomain" xlink:label="us-gaap_LineOfCreditFacilityLenderDomain_635340383948891774"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" order="1" xlink:from="us-gaap_LineOfCreditFacilityAxis" xlink:to="us-gaap_LineOfCreditFacilityLenderDomain_635340383948891774" use="optional"/>
    <loc xlink:type="locator" xlink:href="idxx-20140331.xsd#idxx_InterestRateSwapEffectiveOnMarchThirtyTwoThousandTwelveMember" xlink:label="idxx_InterestRateSwapEffectiveOnMarchThirtyTwoThousandTwelveMember"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_LineOfCreditFacilityLenderDomain" xlink:to="idxx_InterestRateSwapEffectiveOnMarchThirtyTwoThousandTwelveMember" priority="1" use="optional"/>
    <loc xlink:type="locator" xlink:href="idxx-20140331.xsd#idxx_InterestRateSwapEffectiveOnMarchTwentyEightTwoThousandThirteenMember" xlink:label="idxx_InterestRateSwapEffectiveOnMarchTwentyEightTwoThousandThirteenMember"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_LineOfCreditFacilityLenderDomain" xlink:to="idxx_InterestRateSwapEffectiveOnMarchTwentyEightTwoThousandThirteenMember" priority="1" use="optional"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_DerivativeLineItems" xlink:label="us-gaap_DerivativeLineItems"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" order="1" xlink:from="us-gaap_DerivativeLineItems" xlink:to="us-gaap_LineOfCreditFacilityTable" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_CashFlowHedgeGainLossToBeReclassifiedWithinTwelveMonths" xlink:label="us-gaap_CashFlowHedgeGainLossToBeReclassifiedWithinTwelveMonths"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_DerivativeLineItems" xlink:to="us-gaap_CashFlowHedgeGainLossToBeReclassifiedWithinTwelveMonths" priority="1" use="optional"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_MaximumLengthOfTimeForeignCurrencyCashFlowHedge" xlink:label="us-gaap_MaximumLengthOfTimeForeignCurrencyCashFlowHedge"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_DerivativeLineItems" xlink:to="us-gaap_MaximumLengthOfTimeForeignCurrencyCashFlowHedge" priority="1" use="optional"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_DerivativeFixedInterestRate" xlink:label="us-gaap_DerivativeFixedInterestRate"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_DerivativeLineItems" xlink:to="us-gaap_DerivativeFixedInterestRate" priority="1" use="optional"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_DerivativeAmountOfHedgedItem" xlink:label="us-gaap_DerivativeAmountOfHedgedItem"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="us-gaap_DerivativeLineItems" xlink:to="us-gaap_DerivativeAmountOfHedgedItem" priority="1" use="optional"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.sec.gov/invest/2013/invest-2013-01-31.xsd#invest_DerivativeNotionalAmount" xlink:label="invest_DerivativeNotionalAmount"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="6" xlink:from="us-gaap_DerivativeLineItems" xlink:to="invest_DerivativeNotionalAmount" priority="1" use="optional"/>
  </definitionLink>
  <definitionLink xlink:role="http://www.idexx.com/role/DisclosureDerivativeInstrumentsAndHedgingScheduleOfFairValuesAndBalanceSheetClassificationsOfDerivativesDesignatedAsHedgingInstrumentsDetails" xlink:type="extended" xlink:title="41504 - Disclosure - Derivative Instruments And Hedging (Schedule Of Fair Values And Balance Sheet Classifications Of Derivatives Designated As Hedging Instruments) (Details)">
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_FairValuesDerivativesBalanceSheetLocationByDerivativeContractTypeByHedgingDesignationTable" xlink:label="us-gaap_FairValuesDerivativesBalanceSheetLocationByDerivativeContractTypeByHedgingDesignationTable"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_HedgingDesignationAxis" xlink:label="us-gaap_HedgingDesignationAxis"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="1" xlink:from="us-gaap_FairValuesDerivativesBalanceSheetLocationByDerivativeContractTypeByHedgingDesignationTable" xlink:to="us-gaap_HedgingDesignationAxis" use="optional"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_HedgingDesignationDomain" xlink:label="us-gaap_HedgingDesignationDomain"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_HedgingDesignationAxis" xlink:to="us-gaap_HedgingDesignationDomain" use="optional"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_HedgingDesignationDomain" xlink:label="us-gaap_HedgingDesignationDomain_635340383949047775"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" order="1" xlink:from="us-gaap_HedgingDesignationAxis" xlink:to="us-gaap_HedgingDesignationDomain_635340383949047775" use="optional"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_DesignatedAsHedgingInstrumentMember" xlink:label="us-gaap_DesignatedAsHedgingInstrumentMember"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_HedgingDesignationDomain" xlink:to="us-gaap_DesignatedAsHedgingInstrumentMember" use="optional"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_DerivativeInstrumentRiskAxis" xlink:label="us-gaap_DerivativeInstrumentRiskAxis"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="2" xlink:from="us-gaap_FairValuesDerivativesBalanceSheetLocationByDerivativeContractTypeByHedgingDesignationTable" xlink:to="us-gaap_DerivativeInstrumentRiskAxis" use="optional"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_DerivativeContractTypeDomain" xlink:label="us-gaap_DerivativeContractTypeDomain"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_DerivativeInstrumentRiskAxis" xlink:to="us-gaap_DerivativeContractTypeDomain" use="optional"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ForeignExchangeContractMember" xlink:label="us-gaap_ForeignExchangeContractMember"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_DerivativeContractTypeDomain" xlink:to="us-gaap_ForeignExchangeContractMember" use="optional"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_InterestRateSwapMember" xlink:label="us-gaap_InterestRateSwapMember"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_DerivativeContractTypeDomain" xlink:to="us-gaap_InterestRateSwapMember" use="optional"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_BalanceSheetLocationAxis" xlink:label="us-gaap_BalanceSheetLocationAxis"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="3" xlink:from="us-gaap_FairValuesDerivativesBalanceSheetLocationByDerivativeContractTypeByHedgingDesignationTable" xlink:to="us-gaap_BalanceSheetLocationAxis" use="optional"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_BalanceSheetLocationDomain" xlink:label="us-gaap_BalanceSheetLocationDomain"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_BalanceSheetLocationAxis" xlink:to="us-gaap_BalanceSheetLocationDomain" use="optional"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_BalanceSheetLocationDomain" xlink:label="us-gaap_BalanceSheetLocationDomain_635340383949047775"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" order="1" xlink:from="us-gaap_BalanceSheetLocationAxis" xlink:to="us-gaap_BalanceSheetLocationDomain_635340383949047775" use="optional"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_OtherCurrentAssetsMember" xlink:label="us-gaap_OtherCurrentAssetsMember"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_BalanceSheetLocationDomain" xlink:to="us-gaap_OtherCurrentAssetsMember" priority="1" use="optional"/>
    <loc xlink:type="locator" xlink:href="idxx-20140331.xsd#idxx_OtherLongTermAssetsNetMember" xlink:label="idxx_OtherLongTermAssetsNetMember"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_BalanceSheetLocationDomain" xlink:to="idxx_OtherLongTermAssetsNetMember" priority="1" use="optional"/>
    <loc xlink:type="locator" xlink:href="idxx-20140331.xsd#idxx_AccruedExpensesMember" xlink:label="idxx_AccruedExpensesMember"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_BalanceSheetLocationDomain" xlink:to="idxx_AccruedExpensesMember" priority="1" use="optional"/>
    <loc xlink:type="locator" xlink:href="idxx-20140331.xsd#idxx_OtherLongTermLiabilitiesMember" xlink:label="idxx_OtherLongTermLiabilitiesMember"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_BalanceSheetLocationDomain" xlink:to="idxx_OtherLongTermLiabilitiesMember" priority="1" use="optional"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_DerivativesFairValueLineItems" xlink:label="us-gaap_DerivativesFairValueLineItems"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" order="1" xlink:from="us-gaap_DerivativesFairValueLineItems" xlink:to="us-gaap_FairValuesDerivativesBalanceSheetLocationByDerivativeContractTypeByHedgingDesignationTable" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_DerivativeFairValueOfDerivativeAsset" xlink:label="us-gaap_DerivativeFairValueOfDerivativeAsset"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_DerivativesFairValueLineItems" xlink:to="us-gaap_DerivativeFairValueOfDerivativeAsset" priority="1" use="optional"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_DerivativeFairValueOfDerivativeLiability" xlink:label="us-gaap_DerivativeFairValueOfDerivativeLiability"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_DerivativesFairValueLineItems" xlink:to="us-gaap_DerivativeFairValueOfDerivativeLiability" priority="1" use="optional"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_DerivativeFairValueOfDerivativeAssetAmountNotOffsetAgainstCollateral" xlink:label="us-gaap_DerivativeFairValueOfDerivativeAssetAmountNotOffsetAgainstCollateral"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_DerivativesFairValueLineItems" xlink:to="us-gaap_DerivativeFairValueOfDerivativeAssetAmountNotOffsetAgainstCollateral" priority="1" use="optional"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_DerivativeAssets" xlink:label="us-gaap_DerivativeAssets"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="us-gaap_DerivativesFairValueLineItems" xlink:to="us-gaap_DerivativeAssets" priority="1" use="optional"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_DerivativeLiabilities" xlink:label="us-gaap_DerivativeLiabilities"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="6" xlink:from="us-gaap_DerivativesFairValueLineItems" xlink:to="us-gaap_DerivativeLiabilities" priority="1" use="optional"/>
  </definitionLink>
  <definitionLink xlink:role="http://www.idexx.com/role/DisclosureDerivativeInstrumentsAndHedgingGainLossRecognizedInOtherComprehensiveIncomeOnDerivativeInstrumentsEffectivePortionDetails" xlink:type="extended" xlink:title="41505 - Disclosure - Derivative Instruments And Hedging (Gain (Loss) Recognized In Other Comprehensive Income On Derivative Instruments (Effective Portion)) (Details)">
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipByIncomeStatementLocationByDerivativeInstrumentRiskTable" xlink:label="us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipByIncomeStatementLocationByDerivativeInstrumentRiskTable"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_HedgingDesignationAxis" xlink:label="us-gaap_HedgingDesignationAxis"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="1" xlink:from="us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipByIncomeStatementLocationByDerivativeInstrumentRiskTable" xlink:to="us-gaap_HedgingDesignationAxis" use="optional"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_HedgingDesignationDomain" xlink:label="us-gaap_HedgingDesignationDomain"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_HedgingDesignationAxis" xlink:to="us-gaap_HedgingDesignationDomain" use="optional"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_DesignatedAsHedgingInstrumentMember" xlink:label="us-gaap_DesignatedAsHedgingInstrumentMember"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_HedgingDesignationDomain" xlink:to="us-gaap_DesignatedAsHedgingInstrumentMember" use="optional"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis" xlink:label="us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="2" xlink:from="us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipByIncomeStatementLocationByDerivativeInstrumentRiskTable" xlink:to="us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis" use="optional"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_HedgingRelationshipDomain" xlink:label="us-gaap_HedgingRelationshipDomain"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis" xlink:to="us-gaap_HedgingRelationshipDomain" use="optional"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_HedgingRelationshipDomain" xlink:label="us-gaap_HedgingRelationshipDomain_635340383949203776"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" order="1" xlink:from="us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis" xlink:to="us-gaap_HedgingRelationshipDomain_635340383949203776" use="optional"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_CashFlowHedgingMember" xlink:label="us-gaap_CashFlowHedgingMember"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_HedgingRelationshipDomain" xlink:to="us-gaap_CashFlowHedgingMember" use="optional"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_DerivativeInstrumentRiskAxis" xlink:label="us-gaap_DerivativeInstrumentRiskAxis"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="3" xlink:from="us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipByIncomeStatementLocationByDerivativeInstrumentRiskTable" xlink:to="us-gaap_DerivativeInstrumentRiskAxis" use="optional"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_DerivativeContractTypeDomain" xlink:label="us-gaap_DerivativeContractTypeDomain"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_DerivativeInstrumentRiskAxis" xlink:to="us-gaap_DerivativeContractTypeDomain" use="optional"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ForeignExchangeContractMember" xlink:label="us-gaap_ForeignExchangeContractMember"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_DerivativeContractTypeDomain" xlink:to="us-gaap_ForeignExchangeContractMember" use="optional"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_InterestRateSwapMember" xlink:label="us-gaap_InterestRateSwapMember"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_DerivativeContractTypeDomain" xlink:to="us-gaap_InterestRateSwapMember" use="optional"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_DerivativeInstrumentsGainLossLineItems" xlink:label="us-gaap_DerivativeInstrumentsGainLossLineItems"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" order="1" xlink:from="us-gaap_DerivativeInstrumentsGainLossLineItems" xlink:to="us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipByIncomeStatementLocationByDerivativeInstrumentRiskTable" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_DerivativeInstrumentsGainLossRecognizedInOtherComprehensiveIncomeEffectivePortionNet" xlink:label="us-gaap_DerivativeInstrumentsGainLossRecognizedInOtherComprehensiveIncomeEffectivePortionNet"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_DerivativeInstrumentsGainLossLineItems" xlink:to="us-gaap_DerivativeInstrumentsGainLossRecognizedInOtherComprehensiveIncomeEffectivePortionNet" priority="1" use="optional"/>
  </definitionLink>
</linkbase>