Flow cytometry analysis of TfR1 (CD71) expression in bone marrow erythroid cells. Selection of the red cell population by gating with side scatter (SSC-height) and forward scatter (FSC-height) allowed identification of 3 stages of erythroid differentiation: small (I, RBC), intermediate (II, intermediate normoblasts), and large (III, early normoblasts) cells. Bone marrow cells were analyzed by FACS at each stage of differentiation for transferrin receptor (CD71) and Ter-119 expression in BALB/c fch/fch mice and their +/+ control littermates. No significant difference was found between the 2 groups for CD71 expression.