In 1959 we discovered that a hemolytic, anemia-inducing substance is produced in the animals exposed to X-rays. Since then we have found that when this substnce is injeted intravenously into animals, there occur disturbances in the blood, spleen and bone marrow. And also it has become clear that this substance brings about Heinz's body appearance in erythrocytes. As Heinz's body also appears in cancer anemia and it is transformed into hemolysin, it may be assumed that the hemolytic, anemia-inducing substance is contained also in cancer tissue. Upon such assumption we have compared the hemolytic capacity of the extract obtained from the fresh gastric cancer tissue resscted at operation with that of the extract from normal gastric tissue. As the result, we have recognized that this hemolytic, anemia-inducing substance is contained considerably in cancer tissue.