The effect of a single oral dose of omeprazole (90 mg) on gastric emptying was assessed with a dual isotope scintigraphic technique in eight patients with a history of duodenal ulcer disease. Omeprazole had no significant effect on solid or liquid gastric emptying. The bioavailability (AUC0-2 h) of omeprazole in all patients was greater than that required for total suppression of acid secretion. No adverse clinical or laboratory effects were observed.