content: <?xml version="1.0" encoding="UTF-8"?><edgarSubmission xmlns="http://www.sec.gov/edgar/ownership" xmlns:com="http://www.sec.gov/edgar/common">
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      <submissionType>144</submissionType>
      <filerInfo>
        <filer>
          <filerCredentials>
            <cik>0001606030</cik>
            <ccc>XXXXXXXX</ccc>
          </filerCredentials>
        </filer>
        <liveTestFlag>LIVE</liveTestFlag>
  
  
  
      </filerInfo>
    </headerData>
    <formData>
      <issuerInfo>
        <issuerCik>0000730272</issuerCik>
        <issuerName>REPLIGEN CORP</issuerName>
        <secFileNumber>000-14656</secFileNumber>
        <issuerAddress>
          <com:street1>41 SEYON STREET</com:street1>
          <com:street2>BUILDING 1, SUITE 100</com:street2>
          <com:city>WALTHAM</com:city>
          <com:stateOrCountry>MA</com:stateOrCountry>
          <com:zipCode>02453</com:zipCode>
        </issuerAddress>
        <issuerContactPhone>7814499560</issuerContactPhone>
        <nameOfPersonForWhoseAccountTheSecuritiesAreToBeSold>Hunt Anthony</nameOfPersonForWhoseAccountTheSecuritiesAreToBeSold>
        <relationshipsToIssuer>
          <relationshipToIssuer>Director</relationshipToIssuer>
        </relationshipsToIssuer>
      </issuerInfo>
      <securitiesInformation>
        <securitiesClassTitle>Common</securitiesClassTitle>
        <brokerOrMarketmakerDetails>
          <name>Fidelity Brokerage Services LLC</name>
          <address>
            <com:street1>900 Salem Street</com:street1>
            <com:city>Smithfield</com:city>
            <com:stateOrCountry>RI</com:stateOrCountry>
            <com:zipCode>02917</com:zipCode>
          </address>
        </brokerOrMarketmakerDetails>
        <noOfUnitsSold>26756</noOfUnitsSold>
        <aggregateMarketValue>4024637.52</aggregateMarketValue>
        <noOfUnitsOutstanding>56148556</noOfUnitsOutstanding>
        <approxSaleDate>03/17/2025</approxSaleDate>
        <securitiesExchangeName>NASDAQ</securitiesExchangeName>
      </securitiesInformation>
      <securitiesToBeSold>
        <securitiesClassTitle>Common</securitiesClassTitle>
        <acquiredDate>03/17/2025</acquiredDate>
        <natureOfAcquisitionTransaction>Options Granted - 03/01/2018</natureOfAcquisitionTransaction>
        <nameOfPersonfromWhomAcquired>Issuer</nameOfPersonfromWhomAcquired>
        <isGiftTransaction>N</isGiftTransaction>
        <amountOfSecuritiesAcquired>5000</amountOfSecuritiesAcquired>
        <paymentDate>03/17/2025</paymentDate>
        <natureOfPayment>Cash</natureOfPayment>
      </securitiesToBeSold>
      <securitiesToBeSold>
        <securitiesClassTitle>Common</securitiesClassTitle>
        <acquiredDate>03/17/2025</acquiredDate>
        <natureOfAcquisitionTransaction>Options Granted - 02/28/2019</natureOfAcquisitionTransaction>
        <nameOfPersonfromWhomAcquired>Issuer</nameOfPersonfromWhomAcquired>
        <isGiftTransaction>N</isGiftTransaction>
        <amountOfSecuritiesAcquired>21756</amountOfSecuritiesAcquired>
        <paymentDate>03/17/2025</paymentDate>
        <natureOfPayment>Cash</natureOfPayment>
      </securitiesToBeSold>
      <nothingToReportFlagOnSecuritiesSoldInPast3Months>Y</nothingToReportFlagOnSecuritiesSoldInPast3Months>
      <noticeSignature>
        <noticeDate>03/17/2025</noticeDate>
        <planAdoptionDates>
          <planAdoptionDate>12/09/2024</planAdoptionDate>
        </planAdoptionDates>
        <signature>/s/ Margaret Campbell, as a duly authorized representative of Fidelity Brokerage Services LLC, as attorney-in-fact for Anthony J. Hunt</signature>
      </noticeSignature>
    </formData>
  </edgarSubmission>
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text: 144
  0001606030
  XXXXXXXX
  LIVE
  0000730272
  REPLIGEN CORP
  000-14656
  41 SEYON STREET
  BUILDING 1, SUITE 100
  WALTHAM
  MA
  02453
  7814499560
  Hunt Anthony
  Director
  Common
  Fidelity Brokerage Services LLC
  900 Salem Street
  Smithfield
  RI
  02917
  26756
  4024637.52
  56148556
  03/17/2025
  NASDAQ
  Common
  03/17/2025
  Options Granted - 03/01/2018
  Issuer
  N
  5000
  03/17/2025
  Cash
  Common
  03/17/2025
  Options Granted - 02/28/2019
  Issuer
  N
  21756
  03/17/2025
  Cash
  Y
  03/17/2025
  12/09/2024
  /s/ Margaret Campbell, as a duly authorized representative of Fidelity Brokerage Services LLC, as attorney-in-fact for Anthony J. Hunt