The ability of peripheral blood monocytes, granulocytes and resident peritoneal macrophages to generate hydrogen peroxide in response to concanavalin A was enhanced by a single intravenous injection of macrophage colony-stimulating factor (M-CSF) of recombinant human type in AKR mice. In response to phorbol myristate acetate, only granulocytes and resident peritoneal macrophages showed the enhanced ability. Phagocytosis by those cells was not stimulated by M-CSF. Surface marker analysis showed an increased expression of F4/80 and Mac1 on monocytes, Mac1 expression on granulocytes and LFA-1 expression on resident peritoneal macrophages. Ia antigen on resident peritoneal macrophages was suppressed by M-CSF. M-CSF can induce monocytes, granulocytes and resident peritoneal macrophages to generate hydrogen peroxide and enhances their maturation in vivo.