Cimetidine therapy has proved to be effective in healing most duodenal ulcers and in reducing the frequency of reulceration. It is unclear if low-dose maintenance therapy is superior to intermittent full-dose therapy in managing patients whose ulcers recur. Cimetidine is the preferred treatment for patients with the Zollinger-Ellison syndrome, and current evidence indicates efficacy in healing benign gastric ulcers. Some patients with reflux esophagitis improve with cimetidine treatment, but the drug cannot be regarded as first-time therapy. Largely circumstantial evidence suggests a role in preventing bleeding from acute gastric erosions and in preventing the acid aspiration syndrome. Cimetidine therapy has not been found to be useful in controlling acute upper gastrointestinal hemorrhage, acute pancreatitis, or several other conditions for which H2 blockade has been advocated.