In two double-blind, randomized German multicentre trials the effects of omeprazole 20 mg mane and ranitidine 150 mg b.i.d. were compared for the first time in 334 outpatients with duodenal ulcer and 184 outpatients with gastric ulcer. In patients with duodenal ulcer endoscopically controlled healing rates after two weeks were 72% with omeprazole and 59% with ranitidine (p = 0.012); after 4 weeks 96 and 92%, resp. were healed (n.s.). In patients with gastric ulcer the healing rates after two, four, and eight weeks were 43, 81, and 95%, respectively, with omeprazole and 45, 80, and 90%, respectively, with ranitidine (n.s.). Smoking impaired healing in duodenal, but not in gastric ulcer. Symptom relief was comparable with both drugs. Serious side effects or clinically relevant changes in laboratory screening results were not detected. - Our results demonstrate for the first time that omeprazole 20 mg mane is superior to ranitidine 150 mg b.i.d. in the short-term treatment of duodenal, but not gastric ulcer.