An increase of organelles occurs at the reticulocytary maturation stage, when compared with the erythroblastic one, in the peripheral blood of embryos and of patients with acquired hemolytic anemia. This increase is due to hemosome formation, in which possibly the final stage of hemoglobin biosynthesis may take place. In animals with posthemorrhagic anemia, biosynthesis does not occur and reticulocytes present only typical mitochondria. Based on these findings, as well as on reticulocyte basophilia, suggestions were done for the introduction of some modifications in the Harris & Kellermeyer16 1970 conception of the erythrocyte maturation.