Thirty-two patients with rheumatoid arthritis and several other rheumatic diseases were entered into a randomized study to investigate the correlation between the pharmacokinetics and clinical effectiveness of Bi-Profenid 150 mg. Each patient was given, in a variable order, one 150 mg Bi-Profenid tablet twice daily for 2 days, and two 50 mg Profenid capsules each morning and noon with one 100 mg suppository each evening for 2 days. Dosage convenience, effectiveness on pain during the second part of the night and resolution of morning stiffness were considered better with Bi-Profenid by 23 patients and with conventional forms by four, while five reported no preference. In 15 patients treated for one month, only 5 reported mild side-effects which did not require withdrawal from the study. The patients' preference appears to be a result of the bioavailability of Bi-Profenid.