Fluorescent-antibody studies in 22 patients out of a total of 40 cases of acute erosive gastritis showed no antibodies to gastric parietal cells. Hence erosive gastritis seems unlikely to be an autoimmune phenomenon. In this series 57.5% of cases belonged to blood group A. This suggests that there is a correlation between the instability of the gastric mucosa and blood group A. The operative mortality in erosive gastritis is high. Operation should be delayed as long as possible in the hope that the bleeding will stop spontaneously. Erosive gastritis may be idiopathic or precipitated by drugs, particularly aspirin. The highest risk was found to occur in those cases where bleeding was drug-induced.