In man, the reflux of duodenal contents into the stomach leads to gastritis and produces a mucosa susceptible to ulceration. This effect, predominantly due to bile acids, was studied in an animal model in which the oral administration of bile (ox bile powder containing a minimum of 45% cholic acid) markedly increased the gastrolesive action of subcutaneous indomethacin in the pylorus-ligated rat. Oral administration of the new antacid almagate (hydrated aluminium-magnesium hydroxycarbonate, Al2Mg6(OH)14 (CO3)2 X 4 H2O, Almax) gave a significant dose-related reduction in the severity of bile-facilitated gastric lesions whereas aluminium hydroxide gel did not. The antiulcer activity of almagate in this model is presumed to be attributable to its ability to sequester and inactivate bile acids at the pH of the stomach contents, an effect which should beneficially contribute to its acid-neutralising property in the treatment of gastritis, peptic ulcer and associated conditions.