Antacid (AA) in a very low dose (88 mmol/day) was compared to the standard 800-mg dose of cimetidine in healing duodenal ulcers. The influence of sex, age, symptom duration at entry, night pain, smoking, coffee consumption, and alcohol on ulcer healing was studied. The antacid was given in two different schedules: group I--20 ml 1 hr after breakfast and at bedtime; group II--10 ml 1 hr after breakfast and lunch and 20 ml at bedtime. Cimetidine (group III) was given in two divided doses: 400 mg 1 hr after breakfast and 400 mg at bedtime. Endoscopic control was performed after four weeks and, if necessary, after eight weeks of treatment. The healing rate after four weeks of treatment was, respectively, for groups I, II, and III, 45.5%, 55.8%, and 69.4% (group I = group II, and group III different from groups I and II). After eight weeks of treatment the healing rate was 61.5%, 80.8%, and 88.0% for groups I, II, and III, respectively (group II = group III, and group I different from groups II and III). Except for group I, smoking did not influence healing rate. Age, sex, symptoms at entry, night pain, and coffee consumption did not influence the treatment results. The authors concluded that the very low dose of magaldrate (88 mmol/day), when administered in three divided doses (10 ml after breakfast and lunch and 20 ml at bedtime) for eight weeks was as effective as 800 mg of cimetidine (400 mg twice a day) in healing duodenal ulcer.