-----BEGIN PRIVACY-ENHANCED MESSAGE-----
Proc-Type: 2001,MIC-CLEAR
Originator-Name: webmaster@www.sec.gov
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MIC-Info: RSA-MD5,RSA,
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 fj+TczW2BoNbMhGpN6AoPw==

<SEC-DOCUMENT>0001005477-03-004564.txt : 20031203
<SEC-HEADER>0001005477-03-004564.hdr.sgml : 20031203
<ACCEPTANCE-DATETIME>20031203114250
ACCESSION NUMBER:		0001005477-03-004564
CONFORMED SUBMISSION TYPE:	4
PUBLIC DOCUMENT COUNT:		1
CONFORMED PERIOD OF REPORT:	20031120
FILED AS OF DATE:		20031203

REPORTING-OWNER:	

	OWNER DATA:	
		COMPANY CONFORMED NAME:			RYAN THOMAS F JR
		CENTRAL INDEX KEY:			0001263366

	FILING VALUES:
		FORM TYPE:		4
		SEC ACT:		1934 Act
		SEC FILE NUMBER:	000-14656
		FILM NUMBER:		031034411

	BUSINESS ADDRESS:	
		STREET 1:		220 BOYLSTON ST
		STREET 2:		APT #9017
		CITY:			BOSTON
		STATE:			MA
		ZIP:			02116
		BUSINESS PHONE:		6174261476

ISSUER:		

	COMPANY DATA:	
		COMPANY CONFORMED NAME:			REPLIGEN CORP
		CENTRAL INDEX KEY:			0000730272
		STANDARD INDUSTRIAL CLASSIFICATION:	BIOLOGICAL PRODUCTS (NO DIAGNOSTIC SUBSTANCES) [2836]
		IRS NUMBER:				042729386
		STATE OF INCORPORATION:			DE
		FISCAL YEAR END:			0331

	BUSINESS ADDRESS:	
		STREET 1:		41 SEYON STREET
		STREET 2:		BUILDING 1, SUITE 100
		CITY:			WALTHAM
		STATE:			MA
		ZIP:			02453
		BUSINESS PHONE:		7814499560

	MAIL ADDRESS:	
		STREET 1:		41 SEYON STREET
		STREET 2:		BUILDING 1, SUITE 100
		CITY:			WALTHAM
		STATE:			MA
		ZIP:			02453
</SEC-HEADER>
<DOCUMENT>
<TYPE>4
<SEQUENCE>1
<FILENAME>edgar123.xml
<DESCRIPTION>FORM 4
<TEXT>
<XML>
<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0201</schemaVersion>

    <documentType>4</documentType>
    <periodOfReport>2003-11-20</periodOfReport>
    <notSubjectToSection16>0</notSubjectToSection16>
    <issuer>
        <issuerCik>0000730272</issuerCik>
        <issuerName>REPLIGEN CORP</issuerName>
        <issuerTradingSymbol>RGEN</issuerTradingSymbol>
    </issuer>

    <reportingOwner>

        <reportingOwnerId>
            <rptOwnerCik>0001263366</rptOwnerCik>
            <rptOwnerName>RYAN THOMAS F JR</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O REPLIGEN CORPORATION</rptOwnerStreet1>
            <rptOwnerStreet2>41 SEYON STREET, BUILDING 1, SUITE 100</rptOwnerStreet2>
            <rptOwnerCity>WALTHAM</rptOwnerCity>
            <rptOwnerState>MA</rptOwnerState>
            <rptOwnerZipCode>02453</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
            <reportingOwnerRelationship>
        <isDirector>1</isDirector>
        <isOfficer>0</isOfficer>
        <isTenPercentOwner>0</isTenPercentOwner>
        <isOther>0</isOther>
    </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>

        <securityTitle>
            <value>Common Stock</value>
        </securityTitle>

        <transactionDate>
            <value>2003-11-20</value>
        </transactionDate>
    <transactionCoding>
        <transactionFormType>4</transactionFormType>
        <transactionCode>P</transactionCode>
        <equitySwapInvolved>0</equitySwapInvolved>
    </transactionCoding>
        <transactionAmounts>

            <transactionShares>
                <value>5000</value>
            </transactionShares>

            <transactionPricePerShare>
                <value>4.9473</value>
            </transactionPricePerShare>

            <transactionAcquiredDisposedCode>
                <value>A</value>
            </transactionAcquiredDisposedCode>
        </transactionAmounts>
        <postTransactionAmounts>

            <sharesOwnedFollowingTransaction>
                <value>15000</value>
            </sharesOwnedFollowingTransaction>
        </postTransactionAmounts>
        <ownershipNature>

            <directOrIndirectOwnership>
                <value>D</value>
            </directOrIndirectOwnership>
        </ownershipNature>
        </nonDerivativeTransaction>

        <nonDerivativeTransaction>

        <securityTitle>
            <value>Common Stock</value>
        </securityTitle>

        <transactionDate>
            <value>2003-11-20</value>
        </transactionDate>
    <transactionCoding>
        <transactionFormType>4</transactionFormType>
        <transactionCode>P</transactionCode>
        <equitySwapInvolved>0</equitySwapInvolved>
    </transactionCoding>
        <transactionAmounts>

            <transactionShares>
                <value>1000</value>
            </transactionShares>

            <transactionPricePerShare>
                <value>4.96</value>
            </transactionPricePerShare>

            <transactionAcquiredDisposedCode>
                <value>A</value>
            </transactionAcquiredDisposedCode>
        </transactionAmounts>
        <postTransactionAmounts>

            <sharesOwnedFollowingTransaction>
                <value>1000</value>
            </sharesOwnedFollowingTransaction>
        </postTransactionAmounts>
        <ownershipNature>

            <directOrIndirectOwnership>
                <value>I</value>
            </directOrIndirectOwnership>

            <natureOfOwnership>
                <value>by Thomas Ryan, Jr., custodian under UGMA for Jameson Ryan</value>
            </natureOfOwnership>
        </ownershipNature>
        </nonDerivativeTransaction>

        <nonDerivativeTransaction>

        <securityTitle>
            <value>Common Stock</value>
        </securityTitle>

        <transactionDate>
            <value>2003-11-26</value>
        </transactionDate>
    <transactionCoding>
        <transactionFormType>4</transactionFormType>
        <transactionCode>P</transactionCode>
        <equitySwapInvolved>0</equitySwapInvolved>
    </transactionCoding>
        <transactionAmounts>

            <transactionShares>
                <value>5000</value>
            </transactionShares>

            <transactionPricePerShare>
                <value>4.7182</value>
            </transactionPricePerShare>

            <transactionAcquiredDisposedCode>
                <value>A</value>
            </transactionAcquiredDisposedCode>
        </transactionAmounts>
        <postTransactionAmounts>

            <sharesOwnedFollowingTransaction>
                <value>20000</value>
            </sharesOwnedFollowingTransaction>
        </postTransactionAmounts>
        <ownershipNature>

            <directOrIndirectOwnership>
                <value>D</value>
            </directOrIndirectOwnership>
        </ownershipNature>
        </nonDerivativeTransaction>

    </nonDerivativeTable>
    <ownerSignature>
        <signatureName>Barbara Burnim Day (Attorney in Fact)</signatureName>
        <signatureDate>2003-12-03</signatureDate>
    </ownerSignature>

</ownershipDocument>

</XML>
</TEXT>
</DOCUMENT>
</SEC-DOCUMENT>
-----END PRIVACY-ENHANCED MESSAGE-----