Abstract
The in vitro uptake of Fe59 by normal human erythrons is described. All the erythroblastic maturation stages and young erythrocytes in bone marrow as well as in circulating blood take up considerable amounts of radioiron. During the earlier phases of the experiment, the iron uptake is maximal in the later baso-philic and early polychromatic elements. Subsequently, the maximum is reached in the orthochromatic stage. Marrow reticulocytes and circulating young erythrocytes take up small quantities of isotope. Mature erythrocytes do not seem capable of so doing. Iron utilization for hemoglobin synthesis appears to be the main function of the erythron.