Abstract In the present studies, we initiated experiments to identify the signal transduction factors involved in activating phagocytosis, oxidative burst, and degranulation following the binding of IgG-opsonized SE to Fc receptors on the surface of avian heterophils. Peripheral blood heterophils were isolated and exposed to known inhibitors of signal transduction pathways for either 20 min (chelerythine, genistein, or verapamil) or 120 min (pertussis toxin) at 39°C. The cells were then stimulated for 30 min at 39°C with SE opsonized with IgG purified from SE-immune chickens. Phagocytosis, luminol-dependent chemiluminescence (LDCL), and β- 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 (66–98%) and verapamil (47–76%) had marked inhibitory effect on LDCL. Chelerythine (13–25%) and genistein (5–25%) had far less biologically significant effects on LDCL. Neither chelerythine nor genistein had a significant effect on degranulation. Verapamil (2–28%) and pertussis toxin (25–29%) had a moderate inhibitory effect on degranulation stimulated by IgG-opsonized SE. As was found with complement receptor mediated activation of heterophils, 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 play 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. The signal transduction inhibitors used in these studies did not affect Fc receptor mediated degranulation by avian heterophils.