The efficacy of ranitidine 150 mg twice daily and Maalox TC three tablets four times daily were compared in patients with endoscopically confirmed duodenal ulcer. Seventy-nine patients were randomly allocated to double-blind, double-dummy treatment, stratified for smokers. Endoscopy was repeated after four weeks. Those unhealed continued treatment for a further two weeks before final endoscopy. Per protocol analysis in 53 patients showed ulcer healing rates at week 4 and at weeks 4 and 6 combined of 78 and 89% on Maalox TC, and of 81 and 91% on ranitidine, respectively. The same analysis gave overall healing rates of 81% in smokers and 100% in nonsmokers, irrespective of treatment. Both treatments provided early ulcer pain relief. Diarrhea was a commoner side effect in patients on Maalox TC. The study showed Maalox TC and ranitidine were equally effective in healing duodenal ulceration.