Cimetidine is an H2-receptor antagonist that is capable of marked suppression of gastric acid and pepsin secretion. Patients with active duodenal ulcer disease treated with cimetidine show improved rates of healing and symptom relief compared with placebo-treated controls. Peptic ulcer and diarrhea of Zollinger-Ellison syndrome and other acid hypersecretory states respond to cimetidine treatment, as may stress ulcers and steatorrhea of patients with pancreatic insuffficiency who have a suboptimol response to oral pancreatin. Effectiveness with gastric ulcer has been less convincing than with duodenal ulcer. In duodenal ulcer disease, cimetidine need not replace less expensive antacid therapy in most cases and is unlikely to replace definitive surgery for suitable candidates.