A double-blind, crossover trial with 40 patients suffering from classic or definite rheumatoid arthritis was undertaken to obtain a clinical evaluation of naproxen in the disease. Each patient received either naproxen (500 mg/day) or placebo for 20 days and was then switched to the other compound for 20 days. For final evaluation, 22 cases were eliminated for various reasons, leaving 18 patients: seven cases of classical rheumatoid arthritis and 11 cases of definite rheumatoid arthritis. Optimum or very good efficacy of the active compound was present in 66.6 per cent of the cases versus 11.1 per cent of the placebo group. Doubtful or nil activity was observed in 66.6 per cent of the cases receiving placebo versus 16.6 per cent for naproxen. In addition, of the 22 cases that were eliminated from the final evaluation, but which were seen for the first ten-day follow-up visit while taking the active drug, optimum or very good efficacy was seen in 13. Therefore, this trial showed that naproxen achieved antiinflammatory and analgesic activity far superior to that observed with placebo.