Six-hundred sixty-seven patients with endoscopically proven peptic ulcer were included in a randomized, multicenter trial to assess the comparative efficacy of sucralfate and cimetidine. One hundred eighty-seven patients with gastric ulcer and 480 patients with duodenal ulcer completed the study. Ulcer healing was evaluated endoscopically at six weeks for duodenal ulcer and at eight weeks for gastric ulcer. Patients with unhealed ulcer at this time were assigned to the other therapy for a second period of six or eight weeks of treatment (crossover). In patients with duodenal gastric ulcer, pain relief and healing were not significantly different in the two groups. Eighty-eight percent of duodenal ulcers and 73 percent of gastric ulcers healed with six weeks of sucralfate treatment. Reported side effects and symptoms, pooled together for duodenal and gastric ulcer, were more significant in the sucralfate group (7.5 percent) than in the cimetidine group (3.7 percent). Constipation was the most frequent symptom recorded. In conclusion, sucralfate and cimetidine are both excellent healing agents for short-term treatment of duodenal and gastric ulcer. Both give rapid relief of symptoms without severe side effects.