The effect of cultured supernatants of non-stimulated and LPS-induced peritoneal macrophages on erythropoiesis in C57BL/6J mice was studied by using the techniques of culture of hemopoietic progenitor cells in vitro. Our results indicate that(l)BFU-E growth is enhanced significantly after addition of either non-stimulated or LPS-induced supernatants of peritoneal macrophages; (2) the supernatants present positive and negative feedback control on CFU-E

growth-low concentration supernatants stimulate CFU-E and high concentration supernatants present inhibition; (3) the LPS-induced supernatants of peritoneal macrophage show stronger activities than non-stimulated supernatants to the proliteration of both BFU-E and CFU-E and(4)the supernatants of the cultured peritoneal macrophage may contain EPO-like

BPA-like stimulating activities

which regulate the proliferation of both BFU-E and CFU-E