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 Quarterly Report of Alnylam Pharmaceuticals,
Inc. (the "Company") on Form 10-Q for the period ending September 30, 2004 as
filed with the Securities and Exchange Commission (the "Report"), I, Barry E.
Greene, Chief Operating Officer and Treasurer of the Company, certify, pursuant
to Section 1350 of Chapter 63 of Title 18, United States Code, 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 result of operations of the
Company.

                                           /s/  Barry E. Greene
                                           -------------------------------------
                                           Barry E. Greene
                                           Chief Operating Officer and Treasurer

November 15, 2004