The author made a comparative study of serum iron and serum copper contents in various leukemias that had been definitely diagnosed by their bone-marrow tissue culture conducted in our department. Simultaneously the author performed the intravenous iron loading tests and the iron-absorption tests with various leukemias, and obtained the following results. However, in the present comparative study on the serum iron and copper, chronic lymphocytic leukemia is excluded as the number of such cases were too small. 1. In comparing the average value of the serum iron content, acute lymphocytic leukemia shows the greatest value, followed by those of acute myelogenous leukemia, monocytic leukemia, and chronic myelogenous leukemia in the descending order mentioned. The serum copper content is greatest in acute lymphocytic leukemia, and in the descending order of monocytic leukemia, acute myelogenous leukemia, and chronic myelogenous leukemia. Judging monocytic leukemia from the standpoint of its serum iron content, this type also proves to be an intermediary type between acute type and chronic type. 2. In the intravenous iron-loading tests and iron-absorption tests of various leukemias the increased content and decreased content in either case proved to be lower. Moreover, the serum copper content by the iron-loading tests shows hardly any change. 3. In the iron-loading tests likewise no difference can be recognized in various types of leukemia.