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                                  EXHIBIT 31.2

              CERTIFICATION OF CHIEF FINANCIAL OFFICER PURSUANT TO
                 SECTION 302 OF THE SARBANES-OXLEY ACT OF 2002)

         I, Peter N. Kellogg, certify that:

         1. I have reviewed this quarterly report of Biogen, Inc.;

         2. Based on my knowledge, this report does not contain any untrue
statement of a material fact or omit to state a material fact necessary to make
the statements made, in light of the circumstances under which such statements
were made, not misleading with respect to the period covered by this report;

         3. Based on my knowledge, the financial statements, and other
financial information included in this report, fairly present in all material
respects the financial condition, results of operations and cash flows of the
registrant as of, and for, the periods presented in this report;

         4. The registrant's other certifying officer(s) and I are
responsible for establishing and maintaining disclosure controls and procedures
(as defined in Exchange Act Rules 13a-15(e) and 15d-15(e)) for the registrant
and have:

         a) designed such disclosure controls and procedures, or
caused such disclosure controls and procedures to be designed under our
supervision, to ensure that material information relating to the registrant,
including its consolidated subsidiaries, is made known to us by others within
those entities, particularly during the period in which this report is being
prepared;

         b) evaluated the effectiveness of the registrant's disclosure controls
and procedures and presented in this report our conclusions about the
effectiveness of the disclosure controls and procedures, as of the end of the
period covered by this report based on such evaluation; and

         c) disclosed in this report any change in the registrant's internal
control over financial reporting that occurred during the registrant's most
recent fiscal quarter (the registrant's fourth fiscal quarter in the case of an
annual report) that has materially affected, or is reasonably likely to
materially affect, the registrant's internal control over financial reporting;
and

         5. The registrant's other certifying officer(s) and I have
disclosed, based on our most recent evaluation of internal control over
financial reporting, to the registrant's auditors and the audit committee of the
registrant's board of directors (or persons performing the equivalent
functions):

         a) all significant deficiencies and material weaknesses in the design
or operation of internal control over financial reporting which are reasonably
likely to adversely affect the registrant's ability to record, process,
summarize and report financial information; and

         b) any fraud, whether or not material, that involves management or
other employees who have a significant role in the registrant's internal control
over financial reporting.

                           Date: July 31, 2003


                           /s/ Peter N. Kellogg
                           -------------------------------
                           Peter N. Kellogg
                           Executive Vice President - Finance
                            and Chief Financial Officer

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