Duodenal ulcer healing was followed by endoscopy in 186 ethoxzolamide-treated patients. Ethoxzolamide was given in doses of 5-10 mg/kg body weight/day in association with Na and K salts to avoid electrolytic losses. A control group of 161 duodenal ulcer patients received the usual doses of antacids and anticholinergics. The clinical course of pain, inhibition of gastric acid secretion and endoscopic healing of ulcers after 15 and 21 days of treatment were followed, together with the incidence of relapses over a 2-year period. Pain disappeared after 4-6 days of treatment in 91% of the ethoxzolamide-treated group and in 13% of the controls. After 10 days of treatment, ethoxzolamide reduced basal HCl output by 98%, in the control no significant secretory changes were recorded. Endoscopy showed healing in 92% of the cases after 15 days of treatment with ethoxzolamide and in 98% after 21 days; in controls, the corresponding figures were 36% and 46% respectively. Relapse rate after 6 months was 5% in the ethoxzolamide-treated patients and 38% in controls; after one year, relapses were endoscopically confirmed in 7% of the cases in the first group and in 51% respectively in controls; the same rate was 11% and 79% respectively after 2 years. Ethoxzolamide is superior to antacids and anticholinergics in healing duodenal ulcers.