The authors report the results of a randomized study in which comparison was made between two different kinds of treatment in patients affected by uncomplicated duodenal ulcer endoscopically diagnosed. The first group was treated with 1 g of cimetidine per day, during a period of four weeks (200 mg three times a day and 400 mg at bedtime); the second with a liquid Al-Mg antacid compound, 210 ml/day 30 ml, 1 and 3 hr after meals and 30 ml before bedtime) for four weeks. Fity-one patients were studied, 27 treated with cimetidine, 24 with antacids. At the end of the four-week period, 21 patients (77.7%) in the cimetidine group and 18 patients (75%) in the antacid group were completely healed. Benign side effects were remarked in both types of treatment, none of which made it necessary to suspend treatment. No significant variation of the basal and peak acid output before and after each kind of treatment was observed, while a slight but significant increase in fasting serum gastrin concentration was noted after treatment in the antacid group.