Sixty-seven patients with endoscopically proven duodenal ulceration were entered into a double-blind study and randomized to treatment with pirenzepine (PZ) (Gastrozepin; Boehringer Ingelheim) 50 mg twice daily or cimetidine (CM) (Tagamet; Smith Kline & French Laboratories) 400 mg twice daily, given 30 minutes before breakfast and supper. Patients underwent endoscopic examination before entry, at 4 weeks, and at 8 weeks if unhealed at 4 weeks. Once healing was achieved, 43 patients were entered into a single-blind maintenance study with either PZ 50 mg at night or CM 400 mg at night according to their original randomization. CM had a slight, but not significant, advantage over PZ after 4 weeks, but the 8-week data showed identical healing rates. The relapse rate appeared to be higher in the PZ-treated group, but this difference was also not significant. It is suggested that the evening dose of PZ be amended to 50 or perhaps 100 mg before bed in the short-term treatment of duodenal ulcer, and that a dose of 100 mg at night be considered for maintenance therapy in certain high-risk populations.