The purpose of this study is to investigate the clinical efficacy and safety of MRA in a double-blind, parallel-group, controlled study using MRA or methotrexate (MTX) in rheumatoid arthritis (RA) patients with MTX administered.

Inclusion criteria

• Diagnosis of RA based on the 1987 classification criteria of the American College of Rheumatology (ACR)
• Disease duration of 6 months or more
• Treated with 8 mg/week of MTX for at least 8 weeks immediately preceding enrollment, and continued on this treatment up to initiation of the study drug
• Active disease at enrollment (less than 2 weeks before initiating treatment with a study drug), Which is defined as having at least 6 tender and 6 swollen joints among 49 and 46 joints stipulated by the Japanese Rheumatism Foundation's Drug Evaluation Committee and ESR at least 30 mm/hr and CRP not less than 1.0 mg/dL

Exclusion criteria

• Assessed as having Class IV Steinbrocker functional activity in the 4 weeks preceding treatment with the study drug

• Treated with infliximab, etanercept or leflunomide in the 12 weeks preceding treatment with the study drug

• Received any of the following therapies in the 2 weeks preceding initiation of treatment with the study drug.

  1. Administration of any DMARD or immunosuppressant other than MTX
  2. Administration of corticosteroids exceeding 10 mg/day as prednisolone
  3. Dose escalation or initiation of corticosteroids

• Received any of the following therapies in the 4 weeks preceding treatment with the study drug

  1. Plasma exchange therapy
  2. Surgical treatment (operation, etc.)