The author studied changes in serum phosphatase and transaminase in the blood diease, especially leukemia, that had been diagnosed as suchmainly by bone-marrow tissue culture and a new hematological technique devised in the Hiraki Clinic of Internal Medicine, and obtained the following results. 1. In leukemia alkaline phosphatase is slightly decreased while acid phosphatase is slightly increased. However, only in monocytic leukemia these phosphatases are generally normal. In transaminase both glutamic oxalacetic transaminase and glutamic pyruvic transaminase are increased, but such increase is marked in acute myelogenous leukemia followed by monocytic leukemia and chromic myelogenous leukemia, while those in lymphocytic leukemia are normal. From these differences it can be assumed that there are differences in the enzyme system mainly acting upon different leucocyte series. 2. In hypoplastic anemia phosphatase is generally at the normal level, but transaminase is increased, suggesting tissue destruction similar to Banti's disease and hemolytic anemia. In contrast to this, transaminase in idopathic hypochromic anemia transaminase is hardly changed. 3. In cancer disease, only a slight decrease in both phosphatase and transaminase can be observed, but in hepatoma and in the cases with meatastasis into the liver, alkaline phosphatase and transaminase increase in parallel to obstructive jaundice. 4. In lymphogranulomatosis so long as jaundice is not accompanied, phosphatase and transaminase are within the normal range, and in idiopathic thrombocytopenic purpura a slight decrease in alkaline phosphatase can be recognized.