Eighty per cent or more of duodenal and gastric ulcers which have healed after a course of treatment with drugs relapse when therapy is discontinued. Only a gastric operation or continuous maintenance treatment with H2-receptor antagonists has so far been shown to produce sustained remission in the majority of patients. Maintenance treatment with drugs is safer than gastric surgery, since the adverse effects of medical therapy are uncommon, mild and reversible while the after-effects of surgery are common and may be severe and irreversible. Ranitidine is preferred to cimetidine because it has no unwanted effects. The maintenance treatment of ulcer patients with ranitidine must be continued for many years and may have to be life-long.