This 3 arm study will compare the safety and efficacy, with regard to reduction of signs and symptoms, of tocilizumab versus placebo, both in combination with methotrexate (MTX). in patients with moderate to severe active rheumatoid arthritis (RA) who currently have an inadequate response to MTX. Patients wil be randomized to receive tocilizumab 4mg/kg iv, tocilizumab 8mg/mg iv, or placebo iv, every 4 weeks; all patients will also receive methotrexate 10-25mg weekly. The anticipated time on study treatment is 3-12 months, and the target sample size is 500+ individuals.

Inclusion Criteria:

• adult patients at least 18 years of age with moderate to severe active RA for at least 6 months;
• inadequate response to a stable dose of MTX;
• patients of reproductive potential must be using reliable methods of contraception.

Exclusion Criteria:

• major surgery (including joint surgery) within 8 weeks before entering study, or planned surgery within 6 months after entering study;
• prior treatment failure with an anti-tumor necrosis factor agent;
• women who are pregnant or breast-feeding.