Sixty-one patients with symptomatic endoscopically confirmed duodenal ulcer, 5 mm or more in diameter, were treated with omeprazole 30 mg once daily in the morning for 4 weeks. Complete ulcer healing was assessed by endoscopy performed after 15 and, if necessary, 29 days of treatment. The healing rate as 83 p. 100 (49/59 patients) after 2 weeks, and 98 p. 100 (58/59 patients) after 4 weeks. Only 5 patients remained symptomatic on day 15. Fifty-six patients did not take any antacid during the course of treatment. There were few adverse effects. No clinically significant changes in laboratory parameters were observed. These results confirm: the remarkable efficiency of omeprazole in short-term treatment of duodenal ulcer, the good tolerance to this drug, at least in short duration treatment.