2007 Research & Development Day Boston, MA May 17, 2007 Fair Disclosure: Under “Reg FD,” the SEC has set out a series of regulations regarding selective disclosure of material non-public information. In an effort to comply with these regulations, we believe it is important to state at the outset that our presentation todaytoday will not address, nor will we answer any questions relating to, material non-public information. The information we plan to share with you today includes only information that is already in the public domain and/or information that is not material. Forward Looking Statements This presentation includes forward-looking statements about: – the size and growth of the markets for our products, – estimates of sales for our products, – our expected filings with regulatory agencies, – the anticipated development and timing of programs in our clinical pipeline,and – Potential new applications for currently marketed products. Forward-looking statements are subject to risks and uncertainties that could cause actual results to differ materially from those that we expect. Important factors that could cause our actual results to differ include our continued dependence on our two principal products, AVONEX and RITUXAN, the uncertainty of success in commercializing other products including the launch of TYSABRI, the occurrence of adverse safety events with our products, the failure to execute our growth strategy successfully or to compete effectively in our markets, our dependence on collaborations over which we may not always have full control, possible adverse impact of government regulation and changes in the availability of reimbursement for our products, problems with our manufacturing processes and our reliance on third parties, fluctuations in our operating results, our ability to protect our intellectual property rights and the cost of doing so, and the risks of doing business internationally. For a description of the risks and uncertainties that could cause our actual results to differ, please refer to the statements under “Risk Factors” in Item 1A in our Annual Report on Form 10-K and subsequent Quarterly Reports on Form 10-Q filed with the Securities and Exchange Commission. These forward-looking statements speak only as of the date of this presentation, and we do not undertake any obligation to publicly update any forward-looking statements, whether as a result of new information, future events, or otherwise. Page 2 May 17, 2007 2007 R&D Day Agenda Introduction Jim Mullen, CEO 8:30 – 8:35 R&D Overview Cecil Pickett, President R&D 8:35 – 8:45 Neurology Al Sandrock, SVP Neurology R&D 8:45 – 9:45 Break 9:45 – 10:00 Immunology Evan Beckman, SVP Immunology R&D 10:00 – 10:50 Hemophilia Alan Bitonti, SVP Syntonix 10:50 – 11:05 Oncology David Parkinson, SVP Oncology R&D 11:05 – 12:00 Wrap Up / Q&A Cecil Pickett, President R&D 12:00 – 12:15 Page 3 May 17, 2007 Jim Mullen CEO Introduction Pipeline Progression since the Merger Pipeline Transitions Research to Development 1st in Human Late Stage Development • Anti-TWEAK mAb • Anti-BR-3 mAb • Lumiliximab CLL • αvβ6 • BIIB14 • Galiximab NHL • BR-3 Fc • HSP90 inhib BIIB021 • BG-12 MS • Anti-BR-3 mAb • Hu anti-CD20 mAb • RITUXAN® Neurology • CD40L PEG-Fab • LTβR-Fc and Immunology • Anti-Cripto DM4 mAb • Anti TAG-72 mAb* • Anti-IGF-1R mAb • CBE-11* • HSP90 inhib 3647 • IFNβ GD* • Neublastin • FcG-FcE* Filings / Approvals • Approval of TYSABRI® for RRMS • Filing of TYSABRI in Crohn’s Disease • Approval of expanded RITUXAN oncology label • Approval of RITUXAN for RA in TNF-IR * Denotes a discontinued program Page 5 May 17, 2007 Leveraging our Existing Assets Oncology Neurology RITUXAN MS NHL Daclizumab MS Galiximab HSP90 Inhibitors MS NHL Solid Tumors BIIB14 Parkinson’s Lumiliximab BG-12 Parkinson’s CLL TYSABRI MS TYSABRI CDP323 Volociximab (M200) Oncology MS MS Solid Tumors BR3-Fc LTβR-Ig Aviptadil RA TYSABRI PAH RA Crohn’s rFactor IX & VIII FUMADERM® Hemophilia Adentri 2nd Generation Psoriasis Heart Failure anti-CD20 BG-12 Immunology Psoriasis RA New Specialty Markets Page 6 May 17, 2007 Select R&D Accomplishments since Merger Pipeline advancements • 2 product launches (TYSABRI in MS and RITUXAN in RA and expanded oncology label) • 4 programs into late stage development • 8 programs into first in human trials • 10 programs from research into development Corporate restructuring to enable external growth • 7 deals completed Hiring of key talent Creation of therapeutic areas to closely link discovery to development Page 7 May 17, 2007 Cecil Pickett, Ph.D. President, Research and Development Research and Development Overview Biogen Idec’s R&D Strengths • Strong R&D fundamentals – World class biotherapeutic discovery and development organization • Focused drug discovery efforts – Neurology – Immunology – Oncology • Strong link between discovery research, clinical development, and strategic business units • Proven track record of discovering and developing innovative molecules • Extensive biologic manufacturing expertise Page 9 May 17, 2007 R&D Strategy and Execution • Focus on the discovery and development of novel therapeutics to address areas of high unmet medical needs – Internal discovery and external business development – Innovative first-in-class molecules as well as best-in-class molecules • Conduct scientifically rigorous clinical proof of concept experiments to make quick go/no decisions • Execute pivotal registration programs with a global clinical operations organization Page 10 May 17, 2007 Opportunities to Improve R&D Expanding our Capabilities Improving Productivity • Broaden our core discovery and • Increase the number of development development capabilities candidate recommendations • Biologics and small molecules • Expand our small molecule capabilities • Internal discoveries and external • Focus on structure-based drug opportunities design • Enhance drug metabolism and • Improve the development process via formulation support for small a high through-put development molecules initiative • Accelerate first in human studies • Accelerate initiation of pivotal clinical studies • Reduce time between phase transitions • Develop a R&D sourcing strategy Page 11 May 17, 2007 2007 R&D Day Agenda Neurology Al Sandrock, M.D., Ph.D. 8:45 – 9:35 Q&A 9:35 – 9:45 Break 9:45 – 10:00 Immunology Evan Beckman, M.D. 10:00 – 10:40 Q&A 10:40 – 10:50 Hemophilia Alan Bitonti, Ph.D. 10:50 – 11:00 Q&A 11:00 – 11:05 Oncology David Parkinson, M.D. 11:05 – 11:50 Q&A 11:50 – 12:00 Wrap Up and Q&A Cecil Pickett, Ph.D. 12:00 – 12:15 Page 12 May 17, 2007 Al Sandrock, M.D., Ph.D. SVP, Neurology R&D Neurology Pipeline Neurology R&D Pipeline Multiple Sclerosis –BG-12 for MS –RITUXAN for MS –Daclizumab for MS –CDP323 (Oral VLA-4) for MS –LINGO for MS –PML Risk Mitigation Other Neurologic Diseases –BIIB14 for Parkinson’s Disease –Neublastin for Neuropathic pain Page 14 May 17, 2007 Stages of MS MS Lesion Types Time since disease onset Inflammation (interferon-sensitive) conduction block, demyelination, “bystander” axonal injury Degeneration (interferon-resistant) loss of neurons/axons Relapsing- Secondary Remitting Progressive Lesion 1. T cells + macrophages Types 2. Type 1 + Ab and complement 3. Distal oligodendrogliopathy 4. Oligodendrocyte apoptosis Page 15 May 17, 2007 Pathophysiology of MS Page 16 May 17, 2007 Neurology Strategy Overview Continue to develop therapeutics to maintains Biogen Idec’s leadership position in the MS market – While MS market is large and competitive, significant unmet patient need still exists – Several mechanisms of action have a part to play in the pathology of MS thus creating the opportunity to develop multiple therapies – Biogen Idec goal is to leverage its significant expertise and KOL network to discover and develop multiple MS therapies Expand beyond MS into other global specialty markets in neurology with significant unmet medical need Page 17 May 17, 2007 BG-12 for Multiple Sclerosis Page 18 May 17, 2007 BG-12 Activates the Nrf2 Pathway Protecting Cells Against Damage Caused by Oxidative Stress Keap1 Nrf2 - Detox Enzymes - Antioxidant Enzymes Nrf2 - NADPH Generating Enzymes Maf - GSH Biosynthesis Enzymes X Jun - Chaperones ATF4 - Ubiquitination/Proteasome Nrf2 ARE - Detoxification Nucleus - Normalization of energy metabolism - Repair/degradation of damaged proteins Page 19 May 17, 2007 BG-12 Activates the Nrf2 Pathway Protecting Cells Against Damage Caused by Oxidative Stress O O O O BG-12 - Detox Enzymes - Antioxidant Enzymes Keap1 Nrf2 - NADPH Generating Enzymes Maf - GSH Biosynthesis Enzymes Jun - Chaperones ATF4 - Ubiquitination/Proteasome Nrf2 ARE Keap1 - Detoxification Nucleus - Normalization of energy metabolism - Repair/degradation of damaged proteins Page 20 May 17, 2007 BG-12 in RRMS Phase 2b Study Design Blinded Placebo-Controlled Blinded Safety-Extension Treatment Phase Phase Screening Placebo BG-12 240 mg tid (720 mg/day) BG-12 120 mg qd (120 mg/day) Randomization BG-12 120 mg tid (360 mg/day) n=256 BG-12 240 mg tid (720 mg/day)* 4 8 12 16 20 24 24 weeks 24 weeks *Patients 120 mg tid during the first week to determine tolerability Page 21 May 17, 2007 BG-12 in RRMS Phase 2b Trial Results New Gd+ Lesions (Weeks 12 to 24) 6 Pre-Specified Primary End Point 5 4 3 69% P<0.001 2 1 n=54 n=59 n=56 n=54 Mean Number of New Gd+ Lesions 0 Placebo 120 mg qd 120 mg tid 240 mg tid Treatment Group Page 22 May 17, 2007 BG-12 in RRMS Phase 2b Trial Results Relapse Efficacy Treatment Group Placebo 120 mg qd 120 mg tid 240 mg tid n=65 n=64 n=64 n=63 Annualized relapse rate 0.66 0.42 0.78 0.44 (95% CI)* (0.43, 1.01) (0.24, 0.71) (0.52, 1.16) (0.26, 0.76)† % relapse-free patients 69 78 64 71 CI=confidence interval; qd=once daily; tid=three times daily *ITT population, rate adjusted for number of relapses in 12 months prior to study †32% reduction vs placebo Page 23 May 17, 2007 Safety Conclusions • B-12 was generally safe and well tolerated.