The erythroblastic island, a distinct anatomical unit consisting of a central macrophage surrounded by a ring of erythroblasts, is a key feature of erythropoiesis in the bone marrow. While a number of functional sequelae for the interaction between the erythroblasts and macrophage have been suggested, much remains to be learned. We suggest that this interaction may play a role in regulated assembly of membrane proteins during erythroid differentiation.