A double-blind, cross-over trial compared the antiinflammatory and analgesic effects as well as tolerability of diclofenac sodium (Voltaren) and ibuprofen. Twenty-four outpatients with rheumatoid arthritis were included. A single-blind placebo period was inserted between the two active treatments. The daily dose of diclofenac sodium was 50 mg bid and that of ibuprofen 400 mg tid. The duration of each treatment period was 14 days. The efficacy was measured by the following criteria: Articular index (Lansbury), morning stiffness, fatigue, pain (measured on a visual analogue scale), consumption of rescue-analgesics, status of the arthritic condition, and patient preference. No significant differences were found between diclofenac sodium and ibuprofen, but regarding consumption of analgesic, global evaluation, rheumatic activity, and activity index, a slight trend towards a better effect of diclofenac sodium was found. The study had an adequate sensitivity as it could distinguish placebo from the active treatments for all parameters evaluated. No patient was withdrawn for unwanted effects. None of the laboratory data showed abnormalities of clinical relevance.