IL-6 is involved in the pathogenesis of rheumatoid arthritis via its broad effects on immune and inflammatory responses. Our aim was to assess the therapeutic effects of blocking IL-6 by inhibition of the Il-6 receptor with tocilizumab in patients with rheumatoid arthritis. In this double-blind, randomised, placebo-controlled parallel group phase III study, 623 patients were randomly assigned to receive tocilizumab 8 mg/kg (n=205), tocilizumab 4mg/kg (214) or placebo (204) intravenously every 4 week, with methotrexate at stable pre-study doses. The primary endpoint was the proportion of patients with 20% improvement according to ACR criteria at week 24. At 24 weeks, ACR 20 responses were seen in more patients receiving tocilizumab than in those receiving placebo. Tocilizumab could be an effective therapeutic approach in patients with moderate to severe active rheumatoid arthritis.