Pirprofen (600 mg, 800 mg) and aspirin (3,600 mg) were compared in 30 outpatients (33-67 yr old) with definite or classical rheumatoid arthritis. After 10 wk of treatment with either pirprofen dose, the number of painful joints, grip strength, and the duration of morning stiffness improved significantly. Only the number of painful joints improved significantly with aspirin. The erythrocyte sedimentation rate decreased with aspirin and 600 mg pirprofen but increased (significantly) with 800 mg pirprofen. The differences in improvement between the 3 treatment groups were not statistically significant. Gastrointestinal disturbances were the most frequently reported side-effects in each treatment group. Central nervous system effects and tinnitus were reported by more patients in the aspirin group than in either of the pirprofen groups.