A Danish multicentre trial assessed the value of the more effective gastric acid inhibition provided by omeprazole, as compared with cimetidine, in promoting ulcer healing and pain relief in patients with prepyloric ulcers. A total of 176 patients were randomly allocated to 6 weeks of treatment with either cimetidine, 200 mg t.d.s. and 400 mg at bedtime, or omeprazole, 30 mg once daily. At 2, 4, and 6 weeks after entry, ulcers healed in a larger proportion of patients treated with omeprazole (54%, 81% and 86%) than in those treated with cimetidine (39%, 73% and 78%) ('intention-to-treat' cohort; p less than 0.05 at 2 weeks using Cochran-Mantel-Haenszel test). A higher proportion of patients on omeprazole became free of pain during the first week of treatment (p less than 0.05). No major clinical or biochemical side-effects were noted. A 6-month follow-up study revealed no significant difference between the recurrence rates after omeprazole or after cimetidine treatment.