The analgesic efficacy of flurbiprofen (Ansaid, Upjohn) and aspirin were compared in a 12-week, double-blind, randomized, parallel, multicenter study of 147 patients with osteoarthritis of the knee. Flurbiprofen (73 patients) was administered two, three, or four times a day in total daily doses of 100, 150, or 200 mg; aspirin (74 patients) was also given two, three, or four times a day in total daily doses of 2,000, 3,000, or 4,000 mg. Flurbiprofen was found effective in controlling pain and other symptoms of osteoarthritis. In general, the flurbiprofen group showed greater improvement in efficacy variables than did the aspirin group. Statistically significant improvements were noted in the flurbiprofen-treated patients for disability at week 12, and in the clinicians' assessment of response to therapy and disability at the final evaluation. Many flurbiprofen-treated patients (46 percent) completing the trial followed a relatively low dosage regimen of 50 mg twice daily for more than half the study. Flurbiprofen was well tolerated, and no significant laboratory abnormalities were detected.