Phase I study designed to determine the safety and tolerability of a single dose of BIIB023 administered intravenously versus placebo to subjects with RA.

Inclusion Criteria:

• Diagnosis of adult onset RA (functional class I-III) for at least 6 months
• Must have been treated with and be tolerating Methotrexate (5-25 mg/week) for 3 months, at a stable dose for at least 4 weeks
• Must have at least 4 swollen and tender joints due to rheumatoid arthritis

Exclusion Criteria:

• History of recurrent infections requiring antibiotic treatment within 12 months
• Serious local infection or systemic infection within 3 months
• Suffering from rheumatic or autoimmune disease other than RA
• History of cancer, heart failure, kidney disease, liver disease, HIV infection, tuberculosis or other serious illness