We conducted a 4-week double-blind randomized controlled multicentre trial to compare low-dose-antacid (AA) therapy (225 meq total neutralizing capacity per day) with therapy using the prostaglandin E1-analogue, misoprostol (MS) (400 micrograms bid), on ulcer healing and relief of symptoms in 100 outpatients with endoscopically proven duodenal ulcer (DU, 49 patients on AA, 51 patients on MS). Of the 100 patients enrolled in the study 96 could be evaluated; 49 received AA, 47 MS. Endoscopies were performed before treatment, 2 and 4 weeks after initiation of treatment. Healing rates of AA- and MS-treatment were 36.7% vs. 25.5% (2 weeks) and 79.6% vs. 74.4% (4 weeks) and did not differ as much as relief of pain during the daytime. Rates of relief of nighttime pain were significantly higher on AA-treatment after 2 weeks of treatment (81.1% vs. 48.6%; p less than 0.05), but not during the later course of treatment. Thus, it can be concluded that low-dose AA-treatment using an aluminum/magnesium hydroxide preparation in tablet form represents an effective and safe therapy for duodenal ulcer.