Diflunisal (Dolobid; Frosst-MSD) is an acetylsalicylic acid (ASA) derivative and has potential advantages over ASA, e.g. a longer half-life, higher potency and better tolerance. It has been shown to be effective as an analgesic in a variety of conditions. In a 12-week double-blind controlled trial diflunisal was compared with naproxen (Naprosyn; Syntex) in patients with rheumatoid arthritis. Suitable efficacy data were only available at week 4 owing to a number of withdrawals from the naproxen group. Both drugs, however, produced improvement in all the indices measured. At week 12 the initial improvement in the diflunisal group was maintained. Side-effects from diflunisal were mainly related to the gastro-intestinal tract but were not of serious nature; tinnitus and deafness did not occur. Diflunisal is an effective analgesic and also has anit-inflammatory action. It is a useful addition to the range of aspirin derivatives available for the treatment of rheumatoid arthritis.