The effect of totally synthetic PAF-acether (1-O-octadecyl-2-O-acetyl-sn-glyceryl-3-phosphorylcholine), 2-lyso PAF-acether (1-O-octadecyl-sn-glyceryl-3-phosphorylcholine) and lyso-phosphatidylcholine on enzyme release and superoxide production from human polymorphonuclear neutrophils (PMN were studied. PMN (2 X 10(6) ml-1) were incubated at 37 degrees C with various concentrations of phospholipids in the absence of cytochalasin B. At 10(-7) M, PAF-acether induced superoxide production and beta-glucuronidase, acid phosphatase and lysosyme release, but not that of cytoplasmic lactic dehydrogenase. In the same condition 2-lyso PAF-acether and lyso-phosphatidylcholine were ineffective. In the presence of phagocytic stimuli PAF-acether enhanced in the range from 10(-7) M to 10(-10) M the enzyme release and only at 10(-7) M the superoxide production. Thus, the capacity of PAF-acether to stimulate PMN, as well as platelet function, indicates a prominent role for this lipid mediator in inflammatory processes.