The purpose of this report is to analyze the difference in occurence of massive gastrointestinal bleeding caused by severe brain damage between 125 cases treated preventively by antacid buffer (Maalox®) therapy and 387 cases without antacid treatment. The antacid buffer therapy consists of complete neutralization of gastric acid with antacid buffer (Maalox®). Maalox® is infused intermittently through the gastric tube and gastric juice was aspirated through the tube to maintain the pH of the aspirate at 7.0 during one week after the onset of the original disease. Among 125 patients, 43 cases were of traumatic intracerebral hematoma, 38 cases of ruptured aneurysm, and 44 cases of hypertensive intracerebral hematoma. In the group treated by antacid therapy only three cases developed the uncontrolable massive gastrointestinal bleeding; one of them had the bleeding following shock caused by severe infection, and in other 2 cases the pH of gastric juce could not be kept nutralized in spite of antacid buffer therapy. In 97 per cent of the group treated by antacid buffer therapy, massive gastrointestinal bleeding was prevented. On the other hand, 47 cases (12.1 %) out of 387 cases without antacid buffer therapy had massive gastric bleeding and died. In hypertensive intracerebral hematoma, 24.6% of them died because of massive gastric bleeding, and 12.8% of the cases of ruptured aneurysm and 8.2% of severe head injury had untreatable gastric bleeding within one week from the onset of original disease. For the prevention of massive gastrointestinal bleeding caused by severe brain damage following hypertensive cerebral hematoma, ruptured aneurysm and severe head injury, the antacid buffer therapy is effective reducing the occurence rate to less than 3 per cent. This result also suggests that the presence of gastric hydrochloric acid plays an important role in the development and perpetuation of gastrointestinal bleeding.