

<!-- RR Donnelley Xcelerate Taxonomy Schema, based on XBRL 2.1  http://www.rrdonnelley.com/ -->
<!-- Version: 6.23.6 -->
<!-- Round: 5 -->
<!-- Creation date: 2016-08-06T00:39:18Z -->
<!-- Copyright (c) 2005-2013 R.R. Donnelley & Sons Company All Rights Reserved. -->
<schema xmlns="http://www.w3.org/2001/XMLSchema"
  xmlns:xbrli="http://www.xbrl.org/2003/instance"
  xmlns:link="http://www.xbrl.org/2003/linkbase"
  xmlns:xlink="http://www.w3.org/1999/xlink"
  xmlns:us-gaap="http://fasb.org/us-gaap/2016-01-31"
  xmlns:us-types="http://fasb.org/us-types/2016-01-31"
  xmlns:ardx="http://www.ardelyx.com/20160630"
  xmlns:nonnum="http://www.xbrl.org/dtr/type/non-numeric"
  xmlns:num="http://www.xbrl.org/dtr/type/numeric"
  xmlns:xbrldt="http://xbrl.org/2005/xbrldt"
  xmlns:country="http://xbrl.sec.gov/country/2016-01-31"
  xmlns:currency="http://xbrl.sec.gov/currency/2016-01-31"
  xmlns:dei="http://xbrl.sec.gov/dei/2014-01-31"
  xmlns:exch="http://xbrl.sec.gov/exch/2016-01-31"
  xmlns:invest="http://xbrl.sec.gov/invest/2013-01-31"
  xmlns:naics="http://xbrl.sec.gov/naics/2011-01-31"
  xmlns:sic="http://xbrl.sec.gov/sic/2011-01-31"
  xmlns:stpr="http://xbrl.sec.gov/stpr/2011-01-31"
  targetNamespace="http://www.ardelyx.com/20160630"
  elementFormDefault="qualified" attributeFormDefault="unqualified">
  <annotation>
    <appinfo>
      <link:roleType roleURI="http://www.ardelyx.com/taxonomy/role/DocumentandEntityInformation" id="DocumentandEntityInformation">
        <link:definition>101 - Document - Document and Entity Information</link:definition>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.ardelyx.com/taxonomy/role/StatementOfFinancialPositionClassified" id="Role_StatementOfFinancialPositionClassified">
        <link:definition>103 - Statement - Condensed Balance Sheets</link:definition>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.ardelyx.com/taxonomy/role/StatementOfFinancialPositionClassifiedParenthetical" id="Role_StatementOfFinancialPositionClassifiedParen">
        <link:definition>104 - Statement - Condensed Balance Sheets (Parenthetical)</link:definition>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.ardelyx.com/taxonomy/role/StatementOfIncome" id="Role_StatementOfIncome">
        <link:definition>105 - Statement - Condensed Statements of Operations and Comprehensive (Loss) Income</link:definition>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.ardelyx.com/taxonomy/role/StatementOfCashFlowsIndirect" id="Role_StatementOfCashFlowsIndirect">
        <link:definition>106 - Statement - Condensed Statements of Cash Flows</link:definition>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.ardelyx.com/taxonomy/role/NotesToFinancialStatementsOrganizationConsolidationBasisOfPresentationBusinessDescriptionAndAccountingPoliciesTextBlock" id="Role_NotesToFinancialStatementsOrganizationConsolidationBasisOfPresentationBusinessDescriptionAndAccountingPoliciesTextBlock">
        <link:definition>107 - Disclosure - Organization and Basis of Presentation</link:definition>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.ardelyx.com/taxonomy/role/NotesToFinancialStatementsSignificantAccountingPoliciesTextBlock" id="Role_NotesToFinancialStatementsSignificantAccountingPoliciesTextBlock">
        <link:definition>108 - Disclosure - Summary of Significant Accounting Policies</link:definition>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.ardelyx.com/taxonomy/role/NotesToFinancialStatementsFairValueDisclosuresTextBlock" id="Role_NotesToFinancialStatementsFairValueDisclosuresTextBlock">
        <link:definition>109 - Disclosure - Fair Value Measurements</link:definition>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.ardelyx.com/taxonomy/role/NotesToFinancialStatementsCollaborativeArrangementDisclosureTextBlock" id="Role_NotesToFinancialStatementsCollaborativeArrangementDisclosureTextBlock">
        <link:definition>110 - Disclosure - Collaboration and Licensing Agreements</link:definition>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.ardelyx.com/taxonomy/role/NotesToFinancialStatementsDisclosureOfCompensationRelatedCostsShareBasedPaymentsTextBlock" id="Role_NotesToFinancialStatementsDisclosureOfCompensationRelatedCostsShareBasedPaymentsTextBlock">
        <link:definition>111 - Disclosure - Stock-Based Compensation</link:definition>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.ardelyx.com/taxonomy/role/NotesToFinancialStatementsEarningsPerShareTextBlock" id="Role_NotesToFinancialStatementsEarningsPerShareTextBlock">
        <link:definition>112 - Disclosure - Net (Loss) Income Per Share</link:definition>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.ardelyx.com/taxonomy/role/NotesToFinancialStatementsAccountsPayableAccruedLiabilitiesAndOtherLiabilitiesDisclosureCurrentTextBlock" id="Role_NotesToFinancialStatementsAccountsPayableAccruedLiabilitiesAndOtherLiabilitiesDisclosureCurrentTextBlock">
        <link:definition>113 - Disclosure - Accrued and Other Liabilities</link:definition>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.ardelyx.com/taxonomy/role/NotesToFinancialStatementsStockholdersEquityNoteDisclosureTextBlock" id="Role_NotesToFinancialStatementsStockholdersEquityNoteDisclosureTextBlock">
        <link:definition>114 - Disclosure - Stockholders Equity</link:definition>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.ardelyx.com/taxonomy/role/NotesToFinancialStatementsSubsequentEventsTextBlock" id="Role_NotesToFinancialStatementsSubsequentEventsTextBlock">
        <link:definition>115 - Disclosure - Subsequent Events</link:definition>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.ardelyx.com/taxonomy/role/NotesToFinancialStatementsSignificantAccountingPoliciesTextBlockPolicies" id="Role_NotesToFinancialStatementsSignificantAccountingPoliciesTextBlockPolicies">
        <link:definition>116 - Disclosure - Summary of Significant Accounting Policies (Policies)</link:definition>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.ardelyx.com/taxonomy/role/NotesToFinancialStatementsFairValueDisclosuresTextBlockTables" id="Role_NotesToFinancialStatementsFairValueDisclosuresTextBlockTables">
        <link:definition>117 - Disclosure - Fair Value Measurements (Tables)</link:definition>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.ardelyx.com/taxonomy/role/NotesToFinancialStatementsDisclosureOfCompensationRelatedCostsShareBasedPaymentsTextBlockTables" id="Role_NotesToFinancialStatementsDisclosureOfCompensationRelatedCostsShareBasedPaymentsTextBlockTables">
        <link:definition>118 - Disclosure - Stock-Based Compensation (Tables)</link:definition>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.ardelyx.com/taxonomy/role/NotesToFinancialStatementsEarningsPerShareTextBlockTables" id="Role_NotesToFinancialStatementsEarningsPerShareTextBlockTables">
        <link:definition>119 - Disclosure - Net (Loss) Income Per Share (Tables)</link:definition>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.ardelyx.com/taxonomy/role/NotesToFinancialStatementsAccountsPayableAccruedLiabilitiesAndOtherLiabilitiesDisclosureCurrentTextBlockTables" id="Role_NotesToFinancialStatementsAccountsPayableAccruedLiabilitiesAndOtherLiabilitiesDisclosureCurrentTextBlockTables">
        <link:definition>120 - Disclosure - Accrued and Other Liabilities (Tables)</link:definition>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.ardelyx.com/taxonomy/role/DisclosureFairValueMeasurementsSummaryOfFairValueMeasurementsOfCompanysFinancialAssets" id="DisclosureFairValueMeasurementsSummaryOfFairValueMeasurementsOfCompanysFinancialAssets">
        <link:definition>121 - Disclosure - Fair Value Measurements - Summary of Fair Value Measurements of Company's Financial Assets (Detail)</link:definition>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.ardelyx.com/taxonomy/role/DisclosureFairValueMeasurementsAdditionalInformation" id="DisclosureFairValueMeasurementsAdditionalInformation">
        <link:definition>122 - Disclosure - Fair Value Measurements - Additional Information (Detail)</link:definition>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.ardelyx.com/taxonomy/role/DisclosureCollaborationAndLicensingAgreementsAdditionalInformation" id="DisclosureCollaborationAndLicensingAgreementsAdditionalInformation">
        <link:definition>123 - Disclosure - Collaboration and Licensing Agreements - Additional Information (Detail)</link:definition>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.ardelyx.com/taxonomy/role/DisclosureStockBasedCompensationSummaryOfStockBasedCompensationExpenseRecognized" id="DisclosureStockBasedCompensationSummaryOfStockBasedCompensationExpenseRecognized">
        <link:definition>124 - Disclosure - Stock-Based Compensation - Summary of Stock-Based Compensation Expense Recognized (Detail)</link:definition>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.ardelyx.com/taxonomy/role/DisclosureStockBasedCompensationAdditionalInformation" id="DisclosureStockBasedCompensationAdditionalInformation">
        <link:definition>125 - Disclosure - Stock-Based Compensation - Additional Information (Detail)</link:definition>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.ardelyx.com/taxonomy/role/DisclosureNetLossIncomePerShareComputationOfBasicAndDilutedEarningsPerShareAttributableToCommonStockholders" id="DisclosureNetLossIncomePerShareComputationOfBasicAndDilutedEarningsPerShareAttributableToCommonStockholders">
        <link:definition>126 - Disclosure - Net (Loss) Income Per Share - Computation of Basic and Diluted Earnings Per Share Attributable to Common Stockholders (Detail)</link:definition>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.ardelyx.com/taxonomy/role/DisclosureNetLossIncomePerShareAdditionalInformation" id="DisclosureNetLossIncomePerShareAdditionalInformation">
        <link:definition>127 - Disclosure - Net (Loss) Income Per Share - Additional Information (Detail)</link:definition>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.ardelyx.com/taxonomy/role/DisclosureAccruedAndOtherLiabilitiesScheduleOfAccruedLiabilitiesAndOtherLiabilities" id="DisclosureAccruedAndOtherLiabilitiesScheduleOfAccruedLiabilitiesAndOtherLiabilities">
        <link:definition>128 - Disclosure - Accrued and Other Liabilities - Schedule of Accrued Liabilities and Other Liabilities (Detail)</link:definition>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.ardelyx.com/taxonomy/role/DisclosureStockholdersEquityAdditionalInformation" id="DisclosureStockholdersEquityAdditionalInformation">
        <link:definition>129 - Disclosure - Stockholders Equity - Additional Information (Detail)</link:definition>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.ardelyx.com/taxonomy/role/DisclosureSubsequentEventsAdditionalInformation" id="DisclosureSubsequentEventsAdditionalInformation">
        <link:definition>130 - Disclosure - Subsequent Events - Additional Information (Detail)</link:definition>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:linkbaseRef xlink:type="simple" xlink:arcrole="http://www.w3.org/1999/xlink/properties/linkbase" xlink:role="http://www.xbrl.org/2003/role/calculationLinkbaseRef" xlink:href="ardx-20160630_cal.xml" xlink:title="Calculation Links, all"/>
      <link:linkbaseRef xlink:type="simple" xlink:arcrole="http://www.w3.org/1999/xlink/properties/linkbase" xlink:role="http://www.xbrl.org/2003/role/definitionLinkbaseRef" xlink:href="ardx-20160630_def.xml" xlink:title="Definition Links, all"/>
      <link:linkbaseRef xlink:type="simple" xlink:arcrole="http://www.w3.org/1999/xlink/properties/linkbase" xlink:role="http://www.xbrl.org/2003/role/labelLinkbaseRef" xlink:href="ardx-20160630_lab.xml" xlink:title="Label Links, all"/>
      <link:linkbaseRef xlink:type="simple" xlink:arcrole="http://www.w3.org/1999/xlink/properties/linkbase" xlink:role="http://www.xbrl.org/2003/role/presentationLinkbaseRef" xlink:href="ardx-20160630_pre.xml" xlink:title="Presentation Links, all"/>
    </appinfo>
  </annotation>
  <import namespace="http://www.xbrl.org/2003/instance" schemaLocation="http://www.xbrl.org/2003/xbrl-instance-2003-12-31.xsd"/>
  <import namespace="http://www.xbrl.org/2003/linkbase" schemaLocation="http://www.xbrl.org/2003/xbrl-linkbase-2003-12-31.xsd"/>
  <import namespace="http://fasb.org/us-types/2016-01-31" schemaLocation="http://xbrl.fasb.org/us-gaap/2016/elts/us-types-2016-01-31.xsd"/>
  <import namespace="http://www.xbrl.org/dtr/type/non-numeric" schemaLocation="http://www.xbrl.org/dtr/type/nonNumeric-2009-12-16.xsd"/>
  <import namespace="http://www.xbrl.org/dtr/type/numeric" schemaLocation="http://www.xbrl.org/dtr/type/numeric-2009-12-16.xsd"/>
  <import namespace="http://xbrl.org/2005/xbrldt" schemaLocation="http://www.xbrl.org/2005/xbrldt-2005.xsd"/>
  <import namespace="http://fasb.org/us-gaap/2016-01-31" schemaLocation="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd"/>
  <import namespace="http://xbrl.sec.gov/country/2016-01-31" schemaLocation="http://xbrl.sec.gov/country/2016/country-2016-01-31.xsd"/>
  <import namespace="http://xbrl.sec.gov/currency/2016-01-31" schemaLocation="http://xbrl.sec.gov/currency/2016/currency-2016-01-31.xsd"/>
  <import namespace="http://xbrl.sec.gov/dei/2014-01-31" schemaLocation="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd"/>
  <import namespace="http://xbrl.sec.gov/exch/2016-01-31" schemaLocation="http://xbrl.sec.gov/exch/2016/exch-2016-01-31.xsd"/>
  <import namespace="http://xbrl.sec.gov/invest/2013-01-31" schemaLocation="http://xbrl.sec.gov/invest/2013/invest-2013-01-31.xsd"/>
  <import namespace="http://xbrl.sec.gov/naics/2011-01-31" schemaLocation="http://xbrl.sec.gov/naics/2011/naics-2011-01-31.xsd"/>
  <import namespace="http://xbrl.sec.gov/sic/2011-01-31" schemaLocation="http://xbrl.sec.gov/sic/2011/sic-2011-01-31.xsd"/>
  <import namespace="http://xbrl.sec.gov/stpr/2011-01-31" schemaLocation="http://xbrl.sec.gov/stpr/2011/stpr-2011-01-31.xsd"/>
  <element name="AccruedClinicalTrialExpenses" id="ardx_AccruedClinicalTrialExpenses" type="xbrli:monetaryItemType" abstract="false" xbrli:periodType="instant" xbrli:balance="credit" nillable="true" substitutionGroup="xbrli:item"/>
  <element name="AccruedContractManufacturingCosts" id="ardx_AccruedContractManufacturingCosts" type="xbrli:monetaryItemType" abstract="false" xbrli:periodType="instant" xbrli:balance="credit" nillable="true" substitutionGroup="xbrli:item"/>
  <element name="AccruedProfessionalAndConsultantFeesCurrent" id="ardx_AccruedProfessionalAndConsultantFeesCurrent" type="xbrli:monetaryItemType" abstract="false" xbrli:periodType="instant" xbrli:balance="credit" nillable="true" substitutionGroup="xbrli:item"/>
  <element name="AstraZenecaMember" id="ardx_AstraZenecaMember" type="nonnum:domainItemType" abstract="true" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item"/>
  <element name="ClassOfWarrantOrRightExpirationDateDescription" id="ardx_ClassOfWarrantOrRightExpirationDateDescription" type="xbrli:stringItemType" abstract="false" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item"/>
  <element name="ClassOfWarrantOrRightNumberOfWarrantsExercised" id="ardx_ClassOfWarrantOrRightNumberOfWarrantsExercised" type="xbrli:sharesItemType" abstract="false" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item"/>
  <element name="ClassOfWarrantOrRightThresholdOwnershipPercentage" id="ardx_ClassOfWarrantOrRightThresholdOwnershipPercentage" type="num:percentItemType" abstract="false" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item"/>
  <element name="CollaborativeArrangementConsideration" id="ardx_CollaborativeArrangementConsideration" type="xbrli:monetaryItemType" abstract="false" xbrli:periodType="instant" xbrli:balance="credit" nillable="true" substitutionGroup="xbrli:item"/>
  <element name="CollaborativeArrangementUpFrontPayment" id="ardx_CollaborativeArrangementUpFrontPayment" type="xbrli:monetaryItemType" abstract="false" xbrli:periodType="instant" xbrli:balance="credit" nillable="true" substitutionGroup="xbrli:item"/>
  <element name="CommonStockIssuanceCostsIncurredDuringNoncashOrPartialNoncashTransaction" id="ardx_CommonStockIssuanceCostsIncurredDuringNoncashOrPartialNoncashTransaction" type="xbrli:monetaryItemType" abstract="false" xbrli:periodType="duration" xbrli:balance="debit" nillable="true" substitutionGroup="xbrli:item"/>
  <element name="DocumentAndEntityInformationAbstract" id="ardx_DocumentAndEntityInformationAbstract" type="xbrli:stringItemType" abstract="true" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item"/>
  <element name="EmployeesAndConsultantsMember" id="ardx_EmployeesAndConsultantsMember" type="nonnum:domainItemType" abstract="true" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item"/>
  <element name="EmployeeStockPurchasePlanMember" id="ardx_EmployeeStockPurchasePlanMember" type="nonnum:domainItemType" abstract="true" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item"/>
  <element name="GrossProceedsFromIssuanceOfCommonStock" id="ardx_GrossProceedsFromIssuanceOfCommonStock" type="xbrli:monetaryItemType" abstract="false" xbrli:periodType="duration" xbrli:balance="debit" nillable="true" substitutionGroup="xbrli:item"/>
  <element name="NetIncomeLossAndComprehensiveIncomeLoss" id="ardx_NetIncomeLossAndComprehensiveIncomeLoss" type="xbrli:monetaryItemType" abstract="false" xbrli:periodType="duration" xbrli:balance="credit" nillable="true" substitutionGroup="xbrli:item"/>
  <element name="WarrantExpirationTerm" id="ardx_WarrantExpirationTerm" type="xbrli:durationItemType" abstract="false" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item"/>
  <element name="WeightedAveragePrivatePlacementWarrantsOutstanding" id="ardx_WeightedAveragePrivatePlacementWarrantsOutstanding" type="xbrli:sharesItemType" abstract="false" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item"/>
</schema>





