In a double-blind trial lasting 6 months, 36 patients with classical or definity rheumatoid arthritis were divided into two groups, one receiving 3x300 mg proquazone/day and the other 2x250 mg naproxen plus one placebo capsule/day. Efficacy parameters were assessed and laboratory tests performed at regular intervals throughout the trial. Both drugs were well tolerated, in that no abnormal changes were found in the results of laboratory tests in either group, and that drug-related side effects, mainly gastrointestinal disturbances, occurred in just over half the cases in each group. Both drugs improved the Lansbury Index, especially grip strength, walking time, and ESR. Proquazone did significantly better than naproxen in improving ESR and nocturnal pain. More therpaeutic successes were recorded with proquazone than with naproxen in the overall assessment at the end of the trial.