BIOGEN INC. — Director's Dealing 2010

Aug 3, 2010

SEC Form 4 — Statement of Changes in Beneficial Ownership

Issuer: BIOGEN IDEC INC. (BIIB)
CIK: 0000875045
Period of Report: 2010-08-02

Reporting Person: MacLean Michael F (SVP, Chief Accounting Officer)

Non-Derivative Transactions

Date	Security	Code	Shares	Price	A/D	Holdings After	Ownership
2010-08-02	Common Stock	S	682	$56.8669	Disposed	20494.4773	Direct
2010-08-02	Common Stock	S	917	$56.8458	Disposed	19577.4773	Direct
2010-08-02	Common Stock	S	2201	$56.8447	Disposed	17376.4773	Direct
2010-08-02	Common Stock	S	907	$56.8677	Disposed	16469.4773	Direct
2010-08-02	Common Stock	S	2047	$56.8304	Disposed	14422.4773	Direct
2010-08-02	Common Stock	S	582	$56.9107	Disposed	13840.4773	Direct
2010-08-02	Common Stock	S	2206	$56.8439	Disposed	11634.4773	Direct

Footnotes

F1: Sale pursuant to a trading plan intended to comply with Rule 10b5-1 of the Securities Exchange Act of 1934.

F2: Includes 534.5306 shares acquired under the Biogen Idec Inc. employee stock purchase plan on 3/31/2010.

F3: Full information regarding the number of shares sold at each separate price will be provided upon request by the SEC staff, the issuer, or a security holder of the issuer.

F4: This represents the weighted average price for shares sold at a range between $56.46 (low) and $57.17 (high).

F5: This represents the weighted average price for shares sold at a range between $56.55 (low) and $57.12 (high).

F6: This represents the weighted average price for shares sold at a range between $56.52 (low) and $57.27 (high).

F7: This represents the weighted average price for shares sold at a range between $56.54 (low) and $57.27 (high).

F8: This represents the weighted average price for shares sold at a range between $56.52 (low) and $57.21 (high).

F9: This represents the weighted average price for shares sold at a range between $56.63 (low) and $57.18 (high).

F10: This represents the weighted average price for shares sold at a range between $56.45 (low) and $57.19 (high).