Ligand-induced cross-linking of Fcγ receptors (FcγR) on neutrophils plays a significant role in their stimulation, shown here by contrasting the responses induced by low valency immune complexes (LICs) and high valency immune complexes (HICs) and by cross-linking LICs in situ (L/Ab) after their addition to the cells. Multiparameter flow cytometry was used to measure immune complex (IC)-elicited changes in cytoplasmic Ca²⁺ concentration and initiation of the oxidative burst simultaneously in the same cell and to correlate these with FcγR occupancy. We have previously shown that subpopulations of neutrophils respond maximally to subsaturating concentrations of HIC; saturating dosages stimulate the entire population. This discrepancy was not due to differences in receptor occupancy. The magnitude of the transient Ca²⁺ increase was independent of the dose of HIC but depended on the dose when an LIC was used. As shown here, L/Ab cross-linking elicited Ca²⁺ responses similar to those observed in HIC-stimulated cells. In contrast, LIC elicited only minimal intracellular ΔpH and no oxidative burst or membrane potential changes at all unless FcγR was cross-linked, accomplished by HIC or by L/Ab. However, azurophilic degranulation, as determined by elastase release, was not observed in cells stimulated by the in situ cross-linking method, whereas the HIC preparation triggered azurophilic degranulation. Thus, some FcγR-mediated neutrophil effector functions such as azurophilic degranulation and oxidative burst initiation have an absolute requirement for FcγR cross-linking, whereas signaling functions such as changes in membrane potential, intracellular pH, and intracellular Ca²⁺ concentration can occur, albeit more slowly and to a lesser extent, if single FcγR are occupied.