One hundred and ten patients who had been entered into an ulcer healing study 2 to 4 years previously were recalled during an 8-week period for clinical assessment and endoscopy. Fifty-five gastric ulcer patients were followed-up after an average period of 21.2 months. Nine of these had undergone gastric surgery; of the remaining 46 patients, recurrent ulceration was found in 16 (35%). Fifty-five patients with duodenal ulcer disease were also followed-up after an average of 35.6 months. Five of these patients had undergone surgery and of the remaining 50, 25 (50%) had a recurrent duodenal ulcer. About one-third of both gastric and duodenal ulcer recurrences were asymptomatic. Smoking had no effect on recurrence rates.