One hundred and twenty-nine patients were studied with regard to healing of duodenal ulcers with 30 mg omeprazole once daily, recurrence rates after 2 and 4 weeks' treatment in patients with ulcers healed after 2 weeks, and recurrences in rapid and slow healers. Cumulative healing rates were 77% and 98% after 2 and 4 weeks, respectively. Eighty-one patients (65%) were without ulcer symptoms after 2 weeks, and 43 (34%) were improved. Seven of 45 patients (16%; 95% confidence limits, 6-30%) with ulcers healed after 2 weeks had relapsed after another 2 weeks of placebo; 3 were asymptomatic. The overall relapse rate after 6 months was 62%. There were no statistically significant differences in relapse rates between 2 and 4 weeks' treatment of patients with ulcers healed after 2 weeks or between rapid and slow healers. Ulcer size, smoking habits, and alcohol consumption were not significantly related to healing or relapse.