A randomized, single-blind study was designed to assess the effect of lansoprazole alone and lansoprazole plus amoxicillin on the healing and eradication rates in Helicobacter pylori-associated peptic ulcer disease. Seventy-nine patients with gastric ulcers and 54 patients with duodenal ulcers were randomly assigned to two treatment groups. Group 1 received lansoprazole 30 mg daily for 8 weeks for gastric ulcers or 6 weeks for duodenal ulcers. Group 2 received the group 1 regimen plus amoxicillin 2 g daily for 2 weeks. Healing rates at 8 weeks for the gastric ulcer patients were 92 and 84% in groups 1 and 2, respectively (p = not significant). Healing rates at 6 weeks for duodenal ulcers were 96% in group 1 and 100% in group 2 (p = not significant). The eradication rates of H. pylori for gastric ulcer patients were 21 and 54% in groups 1 and 2, respectively (p < 0.05). The H. pylori eradication rates for duodenal ulcer patients were 5 and 73% in groups 1 and 2, respectively (p < 0.001). The H. pylori eradication rates in group 2 were significantly higher than in group 1. Lansoprazole was effective for eradicating H. pylori in this study.