It is well known that uremic patients frequently exhibit hemorrhagic lesions of the digestive tract and the recent introduction and progression of the hemodialysis treatment has changed the frequency of occurrence of a variety of gastrointestinal diseases. We have paid much attention on the upper digestive tract lesions of patients undergoing hemodialysis for chronic renal failure and have found that these lesions are predominantly mucosal hemorrhage of the stomach and gastroduodenal ulcers are rare. We have investigated the mechanism of onset of gastric hemorrhagic mucosal lesions focusing on blood flow, oxygen supply and infection of Helicobacter pylori. We conclude that not the blood flow but oxygen supply seems to play an important role and oxygen radicals produced at hemodialysis also may participate in the pathogenesis of mucosal hemorrhage. On the other hand, Helicobacter pylori does not seem to be important, because its infection rate is low among the patients investigated.