A comparison of cimetidine and colloidal bismuth in the initial healing of chronic duodenal ulcer and the recurrence rate over 1 yr after healing induced by both forms of treatment were investigated. Cimetidine was administered in the dose of 200 mg 3 times daily and 400 mg at night and the dose of colloidal bismuth was 5 ml 4 times each day. Fifty-one outpatients with chronic duodenal ulcers proven on endoscopy completed the initial study. At 3 wk, healing was observed in 83% of the cimetidine group and 70% of the colloidal bismuth group (P > 0.10); at 6 wk, 96% of patients in both groups had healed. Thirty-three patients were followed up over 1 yr, 16 having initially been treated with cimetidine and 17 with colloidal bismuth. Two other patients originally treated with cimetidine were followed-up for 6 mo. only. No further treatment was given. Endoscopy was performed at 6 and 12 mo. or earlier if symptoms developed. At 6 mo., 44% of patients in the cimetidine groups had recurred compared to 47% in the colloidal bismuth group (P > 0.5). At 1 yr 75% of patients in the cimetidine group and 76% in the colloidal bismuth group had recurred (P > 0.5). Both agents are equally effective in healing duodenal ulcers and the incidence of recurrence over 1 yr is similar irrespective of whether the initial healing is induced with colloidal bismuth or cimetidine.