Background: The combination of omeprazole and amoxycillin has demonstrated effectiveness with very few side‐effects in the treatment of H. pylori infection, however cure rates have varied widely. The present study addresses the question as to the extent to which the cure rate of H. pylori infection depends on the size of the daily omeprazole dose, and investigates other patient‐related factors that influence treatment success. Methods: In a randomized, controlled and investigator‐blinded trial, 163 hospitalized patients with H. pylori‐associated gastritis were treated with 20 mg omeprazole once daily in the morning, 20 mg omeprazole b.d., 40 mg omeprazole b.d. or 60 mg omeprazole b.d. for 14 days. In addition, all patients received 1000 mg amoxycillin b.d. on days 5–14. Endoscopic and histological examinations were performed prior to treatment, at the end of treatment and 4 weeks after completion of treatment. Results: H. pylori infection was cured in 18 of 40 (45%, 95% CI: 29–62%), in 22 of 39 (56.4%, 95% CI: 40–72%), in 25 of 38 (65.8%, 95% CI: 49–80%), and in 33 of 40 (82.5%, 95% CI: 67–93%) patients, respectively, (PConclusion: The daily dose of omeprazole is an important factor for the success of dual therapy comprising omeprazole and amoxycillin in curing H. pylori infection. Cure of H. pylori infection correlates positively and significantly with the size of the daily omeprazole dose. The combination of high‐dose omeprazole and amoxycillin is an effective and well‐tolerated regimen for the treatment of H. pylori‐associated diseases.