['Omeprazole is less effective in healthy subjects than in patients with duodenal ulcers. The aim of this study was to determine whether Helicobacter pylori augments the pH-increasing effect of omeprazole in patients with duodenal ulcers.', 'In 16 patients with duodenal ulcers, baseline intragastric acidity was measured before and 4-6 weeks after the cure of H. pylori infection. In 17 patients with duodenal ulcers, 24-hour pH metry was performed during treatment with 20 mg omeprazole once daily before as well as after eradication of H. pylori. Intragastric acidity was measured using a glass electrode placed 5 cm below the cardia. H. pylori infection was assessed by [13C] urea breath test, culture, histology, and rapid urease test.', 'H. pylori eradication resulted in marked decrease of the pH-increasing effect of omeprazole (24-hour median gastric pH, 5.5 vs. 3.0; P<0.002) that was most pronounced during nighttime (median gastric pH, 6.4 vs. 2.1; P=0.001). On the other hand, baseline intragastric pH remained unchanged after eradication (median gastric pH, 1.0 vs. 1.1; P=0.5).'] Does helicobacter pylori augment the pH-increasing effect of omeprazole in patients with duodenal ulcer?