Ferrokinetics by Pollycove's method on 2 cases of Chronic myelogenous leukemia were presented in order to study the erythropoietic function and pathogenesis of anemia. The results are as follows. (1) The daily hemoglobin syntheses were slightly elevated. Both the mean effective hemoglobinization time and mean erythron life span were shortened. The maximum net RBC incorporations of 59Fe were decreased. The in vivo surface measurements of radioactivity over liver, spleen, and sacral bone marrow revealed findings consistant with hemolysis and extramedullary hematopoies. (2) Based upon those findings it is assumed that anemia in chronic myelogenous leukemia may result from hemolysis and inadequate compensation to the developing anemia.