A double-blind crossover study was carried out in 24 patients with osteoarthrosis of the hip or knee to compare the efficacy of a 1200 mg tolmetin daily dose with a 600 mg daily dose, each given for 2 weeks. Both regimens were well tolerated and appeared to give satisfactory relief of pain, but no differences in response between the two dosages were noted either because the number of patients involved were small or because the methods of monitoring clinical improvement were not sufficiently sensitive. A further double-blind crossover study was carried out in 40 patients to compare the efficacy of 1200 mg tolmetin daily with 150 mg ketoprofen daily, each drug being given for 2 weeks after an initial 1-week period on placebo. Pain was monitored using a visual analogue line technique and significant differences were found between both active and placebo periods. Analysis of the biochemical monitoring of both trials showed statistically significant rises in blood urea for all active treatment periods. There were no concomitant changes in serum creatinine, suggesting this effect to be extra-renal in origin. In general, side-effect incidence was low; 1 patient withdrew from ketoprofen treatment because of weight increase and urine retention.