-----BEGIN PRIVACY-ENHANCED MESSAGE-----
Proc-Type: 2001,MIC-CLEAR
Originator-Name: webmaster@www.sec.gov
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 TWSM7vrzLADbmYQaionwg5sDW3P6oaM5D3tdezXMm7z1T+B+twIDAQAB
MIC-Info: RSA-MD5,RSA,
 J4xQLudmYpaMD/c7SMd7zlQQwZd9bqs+/FZ6p2/OKfeNTGt6CMUeZkcWzihU8YnL
 fZUq7ilHo6+R+T1LXXKcfQ==

<SEC-DOCUMENT>0001209191-09-010921.txt : 20090223
<SEC-HEADER>0001209191-09-010921.hdr.sgml : 20090223
<ACCEPTANCE-DATETIME>20090223145102
ACCESSION NUMBER:		0001209191-09-010921
CONFORMED SUBMISSION TYPE:	4
PUBLIC DOCUMENT COUNT:		1
CONFORMED PERIOD OF REPORT:	20090223
FILED AS OF DATE:		20090223
DATE AS OF CHANGE:		20090223

REPORTING-OWNER:	

	OWNER DATA:	
		COMPANY CONFORMED NAME:			NOVARTIS AG
		CENTRAL INDEX KEY:			0001114448
		STANDARD INDUSTRIAL CLASSIFICATION:	PHARMACEUTICAL PREPARATIONS [2834]
		FISCAL YEAR END:			1231

	FILING VALUES:
		FORM TYPE:		4
		SEC ACT:		1934 Act
		SEC FILE NUMBER:	000-49839
		FILM NUMBER:		09627762

	BUSINESS ADDRESS:	
		STREET 1:		LICHSTRASSE 35
		CITY:			BASEL SWITZERLAND
		STATE:			V8
		ZIP:			CH 4056

	MAIL ADDRESS:	
		STREET 1:		LICHSTRASSE 35
		CITY:			BASEL SWITZERLAND
		ZIP:			CH 4056

ISSUER:		

	COMPANY DATA:	
		COMPANY CONFORMED NAME:			IDENIX PHARMACEUTICALS INC
		CENTRAL INDEX KEY:			0001093649
		STANDARD INDUSTRIAL CLASSIFICATION:	PHARMACEUTICAL PREPARATIONS [2834]
		IRS NUMBER:				450478605

	BUSINESS ADDRESS:	
		STREET 1:		60 HAMPSHIRE STREET
		STREET 2:		.
		CITY:			CAMBRIDGE
		STATE:			MA
		ZIP:			02139
		BUSINESS PHONE:		(617) 995-9800

	MAIL ADDRESS:	
		STREET 1:		60 HAMPSHIRE STREET
		CITY:			CAMBRIDGE
		STATE:			MA
		ZIP:			02139

	FORMER COMPANY:	
		FORMER CONFORMED NAME:	NOVIRIO PHARMACEUTICALS LTD
		DATE OF NAME CHANGE:	19990820

REPORTING-OWNER:	

	OWNER DATA:	
		COMPANY CONFORMED NAME:			NOVARTIS PHARMA AG
		CENTRAL INDEX KEY:			0001030617

	FILING VALUES:
		FORM TYPE:		4
		SEC ACT:		1934 Act
		SEC FILE NUMBER:	000-49839
		FILM NUMBER:		09627763

	BUSINESS ADDRESS:	
		STREET 1:		LICHTSTRASSE 35
		STREET 2:		CH-4002
		CITY:			BASEL
		STATE:			V8
		BUSINESS PHONE:		212-830-2474

	MAIL ADDRESS:	
		STREET 1:		LICHTSTRASSE 35
		STREET 2:		CH-4002
		CITY:			BASEL
		STATE:			V8

	FORMER NAME:	
		FORMER CONFORMED NAME:	NOVARTIS INC
		DATE OF NAME CHANGE:	19970114
</SEC-HEADER>
<DOCUMENT>
<TYPE>4
<SEQUENCE>1
<FILENAME>c81522_4x0.xml
<DESCRIPTION>MAIN DOCUMENT DESCRIPTION
<TEXT>
<XML>
<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0303</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2009-02-23</periodOfReport>

    <issuer>
        <issuerCik>0001093649</issuerCik>
        <issuerName>IDENIX PHARMACEUTICALS INC</issuerName>
        <issuerTradingSymbol>IDIX</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001114448</rptOwnerCik>
            <rptOwnerName>NOVARTIS AG</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>LICHSTRASSE 35</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>BASEL</rptOwnerCity>
            <rptOwnerState>V8</rptOwnerState>
            <rptOwnerZipCode>CH 4002</rptOwnerZipCode>
            <rptOwnerStateDescription>SWITZERLAND</rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>1</isOther>
            <otherText>Indirect 10% owner</otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001030617</rptOwnerCik>
            <rptOwnerName>NOVARTIS PHARMA AG</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>LICHSTRASSE 35</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>BASEL</rptOwnerCity>
            <rptOwnerState>V8</rptOwnerState>
            <rptOwnerZipCode>Ch 4002</rptOwnerZipCode>
            <rptOwnerStateDescription>SWITZERLAND</rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>1</isOther>
            <otherText>10% owner</otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2009-02-23</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>P</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>5444</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>2.41</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>31314942</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>See footnote</value>
                    <footnoteId id="F1"/>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <derivativeTable></derivativeTable>

    <footnotes>
        <footnote id="F1">These securities are owned directly by Novartis Pharma AG, a direct, wholly-owned subsidiary of Novartis AG. Novartis AG is an indirect beneficial owner of these securities.</footnote>
    </footnotes>

    <ownerSignature>
        <signatureName>/s/ Jurgen Vierkotter</signatureName>
        <signatureDate>2009-02-23</signatureDate>
    </ownerSignature>

    <ownerSignature>
        <signatureName>/s/ Ramon Zapata-Gomez</signatureName>
        <signatureDate>2009-02-23</signatureDate>
    </ownerSignature>
</ownershipDocument>
</XML>
</TEXT>
</DOCUMENT>
</SEC-DOCUMENT>
-----END PRIVACY-ENHANCED MESSAGE-----