The management of peptic ulcer disease with up to 6 years of continuous cimetidine treatment has been studied at four centres in the UK and Ireland. Cimetidine, 1 g daily for up to 12 weeks, was used to heal duodenal or gastric ulceration, alternating with 400 mg each night to maintain remission. After an initial healing phase, 402 patients started maintenance therapy. Classical life-table analyses showed that after 5 years one-quarter of the patients had suffered a symptomatic relapse, about half during the first year of maintenance treatment. Prevalence analyses (reflecting the cyclical nature of H2-antagonist use in peptic ulcer disease) over 6 years show that, on average, over 97% remain free of symptomatic ulceration at any one time. Patients 'lost' to the study due to withdrawal or default may, however, bias the results. A model designed to account for these estimates that during the long-term management of peptic ulcer with cimetidine, on average around 95% of patients remain free of symptomatic ulceration at any one time. Safety studies, including haematological and biochemical testing over the whole period, revealed no previously unknown adverse reaction. Seven patients were withdrawn for events considered to be related to the drug. Eleven patients died; none of the deaths appears to be connected with the treatment. It is concluded that long-term use of cimetidine is effective in the management of peptic ulcer disease, and continuous treatment for up to 6 years has not revealed any previously unknown hazard.