The clinical usefulness of lansoprazole in the healing of gastric and duodenal ulcers, the S2-stage shift rate (white scarring rate), and endoscopic healing rate with respect to degree of gastric mucosal atrophy were investigated. The subjects were 50 gastric ulcer and 37 duodenal ulcer patients. The endoscopic healing rate in patients with gastric ulcers after initial treatment with lansoprazole was 92% after 8 weeks. The S2-shift rate was 38% after 8 weeks. The 8-week healing rate in patients without atrophy was 100% and with atrophy was 92%, although the difference was not statistically significant. The S2-shift rate in patients without atrophy was 42% and in patients with atrophy was slightly lower, at 37%, although the difference was not statistically significant. The endoscopic healing rate in patients with duodenal ulcers was 93% after 6 weeks, and the S2-shift rate was 59%. It is firmly established that atrophic gastric mucosa shows a reduction in mucosal defense factors. However, lansoprazole achieved good endoscopic healing rates and S2-shift rates even in patients with gastric ulcers with atrophic background mucosa.