EXHIBIT 32.2

                CERTIFICATION PURSUANT TO 18 U.S.C. SECTION 1350,
                             AS ADOPTED PURSUANT TO
                  SECTION 906 OF THE SARBANES-OXLEY ACT OF 2002

     In connection with the Annual Report on Form 10-K of Idenix
Pharmaceuticals, Inc. (the "Company") for the year ended December 31, 2004 as
filed with the Securities and Exchange Commission on the date hereof (the
"Report"), the undersigned, David A. Arkowitz, Chief Financial Officer of the
Company, hereby certifies, pursuant to 18 U.S.C. Section 1350, as adopted by
Section 906 of the Sarbanes-Oxley Act of 2002, that:

     (1)  the Report fully complies with the requirements of Section 13(a) or
          15(d) of the Securities Exchange Act of 1934; and

     (2)  the information contained in the Report fairly presents, in all
          material respects, the financial condition and results of operations
          of the Company.

Date: March 17, 2005


                                        /s/ David A. Arkowitz
                                        ----------------------------------------
                                        David A. Arkowitz
                                        Chief Financial Officer

A signed original of this written statement required by Section 906 has been
provided to Idenix Pharmaceuticals, Inc. and will be retained by Idenix
Pharmaceuticals, Inc. and furnished to the Securities and Exchange Commission or
its staff upon request.