The effect of cimetidine on survival was investigated in 181 patients with gastric cancer. Immediately after operation or the decision not to operate, the patients were randomised in double-blind fashion to placebo or cimetidine 400 mg twice daily for two years or until death, with review every three months. Median survival in the cimetidine group was 450 days (range 1-1826) and in the placebo group 316 days (1-1653). The relative survival rates (cimetidine/placebo) were 45%/28% at 1 year, 22%/13% at 2 years, 13%/7% at 3 years, 9%/3% at 4 years, and 2%/0% at 5 years. Survival in the cimetidine group was significantly longer than in the placebo group.