A double-blind trial was carried out in 76 patients with active rheumatoid arthritis to compare the analgesic and anti-inflammatory activity of 3 g. alclofenac with 4.8 g. aspirin daily over a 6-week period. All patients selected showed reversible inflammatory swelling of the finger joints. Of the 60 patients successfully completing the trial, 30 were treated as out-patients and 30 patients received in-patient treatment for approximately the first 2 weeks. Both groups were analysed separately. Treatment was randomised and patients received the drugs in identical tablet form except for the last 16 patients who were transferred to capsules. Results showed that though the activity potential, morning stiffness, grip strength, joint pain and tenderness improved significantly at the end of the 6-week period, there was no statistical difference between the two drugs. However, functional capacity indicated slight superiority of alclofenac over aspirin at a low level of significance. P.I.P. joint swelling showed that both in-patients and out-patients on alclofenac improved significantly (p less than .001)compared to patients in the aspirin group. Laboratory investigations showed no difference between the two drugs as far as changes in serum proteins, serum transaminase, haemoglobin and E.S.R. levels were concerned. However, serum uric acid levels dropped significantly (.05 greater than p greater than .01) with aspirin. The incidence of side-effects was slightly higher in the aspirin group but a high incidence of skin rash (30% approx.) was recorded with alclofenac tablets. No incidence of skin rash was recorded in patients taking alclofenac capsules, but the number of patients taking capsules was too small to make any prediction. It appears from this study that in active rheumatoid arthritis the analgesic and anti-inflammatory activity of 3 g. alclofenac is equivalent to 4.8 g. aspirin, and alclofenac is superior to aspirin in reducing the inflammatory swelling of rheumatoid joints.