One hundred and seven patients with active juxtapyloric ulcers and a history of chronic ulcer disease were treated with cimetidine. After ulcer healing 67 patients were selected for medical management, testing the value of cimetidine maintenance treatment. Time to healing was shorter for patients with duodenal ulcers when compared with those with active prepyloric ulcers. Recurrences were fewer for patients with pure duodenal ulcer disease (DUD) when compared with those with active or previous prepyloric ulcer disease (PUD). Patients whose ulcers were slow to heal and those with active or previous prepyloric ulcers (PUD) required a higher dose of cimetidine for effective control of their disease. All patients with slowly healing ulcers (more than 6 weeks) relapsed with 400 mg cimetidine at night. Among patients with relapse 46% with DUD and 31% with PUD were controlled by increasing cimetidine to 400 mg twice daily. Tests of acid secretion were of no value in predicting the rate of ulcer healing or relapse rate. Pepsin secretion studies, however, were of predictive value for patients with DUD but of indeterminate value for patients with PUD. Long-term cimetidine produced a significant decrease in pentagastrin-stimulated pepsin secretion (without treatment) in both patients with and without relapse. No significant changes in acid secretion were observed. As a result of these studies we recommend a cimetidine maintenance dosage of 400 mg twice a day for all patients whose ulcers are slow to heal on 1 g cimetidine a day and in patients with prepyloric ulcer disease regardless of rate of healing.