Mature polymorphonuclear leukocytes (PMN) are capable of mediating phorbol myristate acetate (PMA)- and antibody (A)-dependent cellular cytotoxicity (DCC) against ox red blood cells (ORBC) by using oxidative means. The purpose of the present study was to investigate the acquirement of these cytotoxic functions during PMN ontogeny, using the promyelocytic HL-60 cell line as a model for PMN differentiation. HL-60 cells were induced to differentiate along the PMN pathway by exposure to dimethyl sulfoxide (DMSO). Uninduced HL-60 cells were found to be completely devoid of PMA-DCC and ADCC activity. DMSO-induced cells progressively acquired the capacity to kill ORBC and to undergo the activation of oxidative metabolic burst when triggered by PMA. Despite approximately 40% of them also were capable of binding IgG-sensitized ORBC, no ADCC activity and respiratory burst activation was observed: this finding indicates that maturing HL-60 cells require a more complete maturation than that induced by DMSO to actually exert ADCC. Together the results suggest that: a. the acquirement of both PMA-DCC and ADCC potential is a post-promyelocytic event; b. the cytotoxicity activating stimuli, PMA and IgG-coated targets, follow different post-receptor transductional pathways to trigger the effector cell lytic systems: only the PMA receptor-linked pathway develops during DMSO-driven differentiation of HL-60 cells.