This 2 arm study will compare the safety and efficacy, with regard to reduction of signs and symptoms, of tocilizumab versus placebo in combination with traditional Disease-Modifying Anti-Rheumatic Drug (DMARD) therapy in patients with moderate to severe active rheumatoid arthritis (RA) who have had an inadequate response to current DMARD therapy. Patients will be randomized to receive tocilizumab 8mg/kg iv or placebo iv every 4 weeks, in conjunction with stable DMARD therapy. The anticipated time on study treatment is 3-12 months, and the target sample size is 500+ individuals.

Inclusion Criteria:

• patients at least 18 years of age with moderate to severe active RA for at least 6 months;
• inadequate response to current anti-rheumatic therapies, including 1 or more traditional DMARDs;
• stable DMARD therapy for at least 8 weeks before entering study;
• 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;
• patients who have previously failed treatment with an anti-tumor necrosis factor agent;
• women who are pregnant or breast-feeding.