Maintenance therapy with either ranitidine or cimetidine has been administered for up to 5 years to several hundred patients suffering from duodenal or gastric ulcer disease. Maintenance treatment prevented symptomatic ulcer relapse in approximately three-quarters of patients over this period of time. About half of symptomatic ulcer relapses occurred during the 1st year of maintenance therapy, and thereafter the symptomatic recurrence rate was extremely low. Potentially the most important effect of maintenance therapy was to reduce the incidence of ulcer complications, particularly haemorrhage (from 6.2% to 0.4% during the 1st year of duodenal ulcer maintenance). Maintenance therapy is therefore likely to reduce ulcer morbidity and to be cost-beneficial in patients who have previously experienced an ulcer complication and are at an increased risk of the same complication in the future. Maintenance therapy with 300 mg ranitidine daily was more effective than 150 mg ranitidine at night in smokers and may be a useful therapeutic option for smokers who relapse during maintenance therapy with 150 mg ranitidine at night or for smokers in whom it is mandatory to prevent ulcer recurrence because of a previous complication. Asymptomatic ulcers occurring during maintenance therapy are clinically benign, and rehealing such ulcers does not alter the subsequent clinical course. Point prevalences of asymptomatic reulceration should not be used when assessing the clinical value of maintenance therapy.