Famotidine (40 mg) and 800 mg cimetidine as single night-time doses were compared in a randomized, double-blind, multicentre study of acute treatment for duodenal ulceration. Fifteen centres recruited 304 patients into the study. Of these, 274 were included for analysis, with 136 receiving famotidine and 138 receiving cimetidine. After 4 weeks, 75% of the patients who received famotidine and 77% of the patients who received cimetidine were healed. At 6 weeks the cumulative healing rates were 91% with famotidine and 87% with cimetidine. Differences between the groups were not significant at 4 or 6 weeks. No significant difference in healing rates between smokers and non-smokers was found. Day and night pain resolved rapidly in both groups. Both treatments were well-tolerated; adverse events were reported in 17 patients on famotidine and 18 on cimetidine, with headache the most frequent event in both groups. Famotidine is effective and well-tolerated in the short-term treatment of duodenal ulcer.