Antacids are widely used for dyspeptic complaints. Until recently, their clinical effect was thought to depend on neutralization of gastric hydrochloric acid. This action depends on several factors such as chemical composition, gastric acid secretion, gastric emptying and interaction with food. However, both high-dose antacid regimens, with a pronounced effect on intragastric acidity, as well as low-dose regimens, with a negligible effect on acidity, have a proven effect in peptic ulcer disease. The effect, even of very low-dose antacid regimens, is similar to that of H-2-receptor antagonist treatment. This supports the hypothesis that antacids promote peptic ulcer healing by modes of action other than acid neutralization.