In a double-blind, dose comparison multicenter trial 115 patients with duodenal ulcer were treated with either 20 or 30 mg oral omeprazole once daily for 4 weeks. There was no difference in the healing rates for the two groups after 2 and 4 weeks. After 2 weeks with 20 and 30 mg healing frequencies were 79.0 and 72.7%, after 4 weeks 96.5 and 92.7%. No difference was observed between the groups in the number of pain episodes during day and night. No side effects to the drug occurred. A daily dose of 20 mg omeprazole may be effective in ulcer therapy.