OBJECTIVE: To assess the efficacy and safety of T-614 versus methotrexate (MTX) in patients with active rheumatoid arthritis (RA). METHODS: In this multicenter, double-blind trial, 489 patients randomly received either T-614 25 mg/day for the first 4 weeks and 50 mg/day for the subsequent 20 weeks (group 1, n = 163), T-614 50 mg/day for 24 weeks (group 2, n = 163), or MTX 10 mg/week for the first 4 weeks and 15 mg/week for the subsequent 20 weeks (n = 163). Clinical and laboratory parameters were analyzed at baseline and at 4, 10, 17, and 24 weeks. RESULTS: After 24 weeks of treatment, the American College of Rheumatology 20% improvement criteria response rate for patients in T-614 group 2 (63.8%) was not statistically significantly different from that for patients receiving MTX treatment (62.0%), and was superior to that for patients in T-614 group 1 (50.9%). The result of the noninferiority analysis indicated that the efficacy of T-614 (50 mg/day) was not lower than that of MTX by <10%. Rheumatoid factor and IgA, IgG, and IgM demonstrated a statistically significant decrease in all groups. Frequently reported adverse events included hematologic disorder, skin reactions, gastrointestinal symptoms, and transient liver enzyme elevations in the T-614 therapy groups. Side effects in the T-614 groups were generally fewer and milder than in the MTX group, except for skin reactions. There were no prominent cardiovascular adverse events and gastrointestinal ulcers found in the T-614 groups. CONCLUSION: Results indicate that T-614 therapy 50 mg/day is effective and well tolerated, and represents a new option for the treatment of patients with active RA.