Two hundred and fifty-four patients with post-operative pain following closed reduction of fractured long bones completed a double-blind study of dipyrone and aspirin. Compared with placebo both active treatments produced significant relief of pain, which was apparent 30 minutes after ingestion and was maintained for the 6-hour duration of the study. Dipyrone 500 mg produced significantly greater pain relief than aspirin 500 mg. Both drugs were generally well tolerated.