Erythroblasts (EBLs) as well as thrombocytes and myelocytes show changes in patients with myelodysplastic syndrome (MDS). The changes include increse in sideroblasts and maturation delay. Expression of the transferrin receptor (TfR) has been known to correlate with stainable iron and cell maturation. To clarify whether the regulation mechanism of TfR on bone marrow EBLs is altered in MDS and acute leukemia (AL), TfR expression on EBL from MDS and AL were measured in individual cells as well as cell morphology, stainable iron granules (SIGs) in EBLs and cellular hemoglobin content using the morphometric method established in our laboratory. Generally, the number of TfR and density of TfR on EBLs decreased along with cell maturation. The density of TfR was negatively correlated with hemoglobin concentration (r＝－0.76), but SIGs showed no significant correlation with TfR density. In a patint with RARS, there was no difference in TfR density between ringed and non-ringed sideroblasts. By contrast, in a patient with AL, the TfR density of EBLs with morphological changes in nucleus was lower than that of normal EBLs. These findings suggest that the regulation mechanism of TfR in MDS was similar to normal subjects in cell maturation, hemogulobin concentration and SIGs, leaving the question why EBLs in MDS contain numerous SIGs in future.