Forty-three patients with active duodenal ulcer and Helicobacter pylori positivity in gastric antrum were randomly assigned to either omeprazole treatment (20 mg once a day) or ranitidine treatment (300 mg once a day) for 28 days. Re-evaluation of the patients (clinical and endoscopic examination and assessments for H pylori detection) was repeated after 2 weeks and at the end of the treatment. Healing rates in the omeprazole group were 40% after 2 weeks and 90% after 4 weeks, in the ranitidine group ulcer healing was recorded in 20% of patients after 2 weeks and in 80% after 4 weeks. Differences between treatments at 2 and 4 weeks were not statistically significant. Clinical response (disappearance of ulcer-related symptoms) was better in the omeprazole group at 2 weeks (p less than 0.05) but not at 4 weeks. At the end of the trial H pylori positivity in gastric antrum disappeared in 95% of the patients treated with omeprazole and in 5% of the patients who received ranitidine (p less than 0.001). The results confirm the effectiveness of omeprazole in short-term treatment of duodenal ulcer and re-emphasize the powerful activity of the drug on H pylori infection.