Aspirin-induced gastritis and gastrointestinal hemorrhage were reviewed and discussed on the basis of currently available literature. Acute hemorrhagic gastritis occurs in from 50% to 70% of all patients taking aspirin, is not directly related to dose size, and can be severe enough to cause death in a few cases. No tolerance appears to ever develop. The mechanism that causes this bleeding is not definite, but the back diffusion of H+ ions accross the gastric barrier seems to bear primary responsibility, with physical erosion, prolonged platelet bleeding, and the effect of low pH values also being possible explanations. There appears to be less acid present in the stomach when bleeding occurs, but this is a masking effect of the aspirin that causes increased absorption of the H+ ions. Factors important in determining pharmaceutical formulation are method of administration, particle size of the aspirin, duration of contact between the drug and the mucosa, presence of buffers in the drug to raise the gastric pH, dissolution rate of the drug in the stomach, and ionization characteristics of the drug itself. Gastrointestinal blood loss caused by aspirin can be minimized by administering the drug in one of these forms:--a dilute solution of acetylsalicylate;--an intravenously injected solution;--a very rapidly dissolving and rapidly absorbed tablet;--a solution with sufficiently large amounts of antacid added;--a fine-grain, highly buffered aspirin tablet;--an enteric-coated tablet that does not dissolve in the stomach; or--an aspirin substitute such as acetaminophen.