EXHIBIT 99.1

                                  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)

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, Inc., a Massachusetts corporation (the
"Company"), does hereby certify, to such officer's knowledge, that:

The Quarterly Report on Form 10-Q for the quarter ended March 31, 2003 (the
"Form 10-Q") 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-Q fairly presents, in all material respects, the
financial condition and results of operations of the Company.



    Dated: April 17, 2003
                                              ---------------------------------
                                              JAMES C. MULLEN
                                              CHAIRMAN, CHIEF EXECUTIVE OFFICER
                                                AND PRESIDENT



    Dated: April 17, 2003
                                              ---------------------------------
                                              PETER N. KELLOGG
                                              EXECUTIVE VICE PRESIDENT - FINANCE
                                                AND CHIEF FINANCIAL OFFICER

The foregoing certification is being furnished solely 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) and is not being filed as part of the Form
10-Q or as a separate disclosure document. A signed original of this written
statement required by section 906 of the Sarbanes-Oxley Act of 2002 has been
provided to Biogen, Inc. and will be retained by Biogen, Inc. and furnished to
the Securities and Exchange Commission upon request.



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