FIRST AMENDMENT TO
THIS AMENDMENT by and between BIOGEN IDEC INC., formerly IDEC Pharmaceuticals Corporation (the
Company), and James C. Mullen (the Executive), dated as of February 7, 2006.
WHEREAS, the Executive and the Company are parties to an Employment Agreement dated as of June
20, 2003 (the June 20, 2003 Agreement); and
WHEREAS, the Executive and the Company desire to amend the June 20, 2003 Agreement as set
NOW, THEREFORE, it is hereby agreed as follows:
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