OBJECTIVE Anti-Helicobacter pylori treatment with combinations of omeprazole and amoxicillin is a promising treatment option. The aim of this study was to investigate whether a daily omeprazole dose of 120 mg combined with amoxicillin would cure H. pylori infection at a rate comparable with that achieved with "triple therapy." METHODS In a double-blind, randomized, controlled, and multicenter trial in Germany, 270 patients with an H. pylori-associated duodenal ulcer were treated with 40 mg omeprazole three times a day and 750 mg amoxicillin three times a day for the first 14 days (n = 139) followed by 20 mg omeprazole once daily until day 42 or with omeprazole plus 750 mg amoxicillin placebo three times a day for the same time period (n = 131). RESULTS Cure rates of H. pylori infection were 91% in the omeprazole plus amoxicillin group, 0% in the omeprazole plus placebo group, and 89% and 0%, respectively, performing an intention-to-treat analysis. Cure of H. pylori infection in patients pretreated with omeprazole was only 58% compared with 95% in patients who were not. The cumulative 12-month relapse rates were 11.3% and 44% in the treatment groups and 1.6% in H. pylori-negative and 49% in H. pylori-positive patients. CONCLUSIONS The combination of 120 mg omeprazole daily and 2.25 g amoxicillin daily with its H. pylori cure rate of around 90% is one of the best tolerated and most effective treatment regimens.