Four studies on ketoprofen [2-(3 Benzoylphenyl) propionic acid, 19583 R.P., Orudis, Profenid N.D.] have been carried out to establish whether it is well tolerated and effective in the treatment of patients with rheumatoid arthritis. Firstly a comprehensive open clinical and biological monitoring study was undertakin in 11 patients who received ketoprofen for an average period of 20 months without any serious or persistent adverse clinical reaction or adverse change in standard laboratory investigations. The second study involved the same patients who were also included in an ophthalmic screening study for drug toxicity. This established that no eye abnormalities attributable to ketoprofen occurred during this period of treatment. These tolerance studies were then followed by two comparative double-blind cross-over trials of ketoprofen in 117 patients with "definite" rheumatoid arthritis. One of them confirmed the significantly superior analgesic effect compared with placebo and showed that the incidence of adverse reactions was similar. The other trial showed that comparing ketoprofen 150 mg daily and indomethacin 100 mg daily the clinical effects of the two drugs were the same in 8 out of 10 indices. Only in severity of pain and rescue drug count was there a significant difference favouring indomethacin. Adverse reactions were more frequent with indomethacin despite prior exclusion from the study of patients known to be intolerant of indomethacin. It was concluded that on this evidence ketoprofen is a clinically active and well tolerated drug which should be valuable in the management of rheumatoid arthritis.