Technical Abstract: We initiated experiments to identify the signal transduction factors involved in phagocytosis, oxidative burst, and degranulation following the binding of IgG-opsonized SE to Fc receptors on the surface of avian heterophils. Heterophils were exposed to known inhibitors of signal transduction pathways and then stimulated for 30 min with Salmonella enteritidis (SE) opsonized with IgG purified from SE-immune chickens. Phagocytosis, luminol-dependent chemiluminescence (LDCL), and beta-D- glucuronidase release were then evaluated in vitro. The G-protein inhibitor, pertussis toxin, the protein kinase C inhibitor, chelerythine, and the Ca** channel blocker, verapamil, markedly reduced phagocytosis in a dose responsive manner. Genistein, a tyrosine kinase inhibitor, had no effect on the phagocytosis of the opsonized SE. Both pertussis toxin and verapamil had marked inhibitory effect on LDCL. Chelerythine and genistein had far less biologically significant effects on LDCL. Neither chelerythine nor genistein had a significant effect on degranulation. Verapamil and pertussis toxin had a moderate inhibitory effect on degranulation stimulated by IgG-opsonized SE. Thus, the binding of Fc receptors by the IgG-SE complex activated distinct signaling pathways that regulate the functional activities of avian heterophils. Pertussis toxin- sensitive, Ca**-dependent, G-proteins and protein kinase C-dependent protein phosphorylation plays a major role in the phagocytosis of IgG opsonized SE. Pertussis toxin-sensitive, Ca**-dependent, G-proteins appear to regulate LDCL following Fc receptor binding.