50 patients with intractable duodenal ulcer were randomly assigned to 4 weeks of treatment with colloidal bismuth subcitrate (CBS) alone (26 patients) or with amoxicillin and metronidazole (24 patients). 5 patients (all on triple therapy) withdrew because of side-effects. In 17 of the 45 patients who completed the treatment, Helicobacter pylori was eradicated, and there was no ulcer relapse during the first 12 months of follow-up. The ulcer relapse rate was significantly higher (17 of 21 [89%]) among patients who remained positive for H pylori. 9 patients who remained positive for H pylori and had ulcer relapses within 6 months of treatment with CBS alone, were subsequently given triple therapy. 7 of the 9 showed H pylori eradication and no relapses within the next 12 months. The 2 patients still H pylori-positive after triple therapy had further ulcer relapses. H pylori eradication, without altering acid output, will become the mainstay of duodenal ulcer treatment because it cures the disease.