This double-blind, placebo-controlled, parallel-group study proves that the duration of activity of a sustained-release preparation of flurbiprofen 200 mg covers a full 24 hour period. In a group of 24 patients with clinically active rheumatoid arthritis a statistically significant increase of pain was noted 37 hours after the last active dose. The increase in disease symptoms was inversely related to the plasma flurbiprofen levels and was rapidly reversed with one active dose of sustained release flurbiprofen.