1 EXHIBIT 10.35 BIOGEN, INC. Supplemental Executive Retirement Plan FIRST AMENDMENT TO THE 4/1/96 RESTATEMENT The Biogen, Inc. Supplemental Executive Retirement Plan ("Plan"), as heretofore amended, is hereby further amended as follows: Section 3.4 is inserted and shall state: "An individual is not considered a Participant for purposes of this Plan if the individual is classified as a consultant or contractor under the Company's or the Company's affiliate's regular personnel classifications and practices, or he is a party to an agreement to provide services to the Company or the Company's affiliate without participating in the Plan, notwithstanding that such individual may be treated as a common law employee for payroll tax or other legal purposes." Date: September 27, 1999 BIOGEN, INC. By: /s/ Frank A. Burke, Jr. --------------------------------- Frank A. Burke, Jr. Vice President - Human Resources