Exhibit 32.1

                        SECTION 906 CEO/CFO CERTIFICATION

        Pursuant to Section 906 of the Sarbanes-Oxley Act of 2002 (Subsections
(a) and (b) of Section 1350, Chapter 63 of Title 18, United States Code) each of
the undersigned officers of Biogen Idec Inc., a Delaware corporation (the
"Company"), does hereby certify, to such officer's knowledge, that:

        The Annual Report on Form 10-K for the year ended December 31, 2003 (the
"Form 10-K") of the Company fully complies with the requirements of Section
13(a) or 15(d) of the Securities Exchange Act of 1934, and the information
contained in the Form 10-K fairly presents, in all material respects, the
financial condition and results of operations of the Company.




        Dated:  March 9, 2004           /s/ James C. Mullen
                                        -------------------------------------
                                        James C. Mullen
                                        Chief Executive Officer and President





        Dated:  March 9, 2004           /s/ Peter N. Kellogg
                                        -------------------------------------
                                        Peter N. Kellogg
                                        Executive Vice President, Finance and
                                          Chief Financial Officer


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