Phagocytosis of whole blood polymorphonuclear leukocytes (PMN) was evaluated following periods of hypoxemia or hypoxemia/reoxygenation. Hypoxemia (O2 saturation 5–20%) significantly increased the percentage of PMN positive for phagocytosis. This effect required mobilization of intracellular Ca2+ stores and was accompanied by a significant increase in CD16, CD32w, and CD35 expression assayed using FITC-labeled Mabs. PMA (10 ng/ml) increased CD32w expression while protein kinase C inhibitors H-7 and staurosporine but not the protein kinase A inhibitor H-9 reversed the effect of hypoxemia on phagocytosis and receptor expression. Further, genistein (tyronsine kinase inhibition) reversed hypoxemia-induced increases in phagocytosis (ID50-50 μM). Reoxygenation (O2 saturation 97–99%) reduced the percentage of PMN positive for phagocytosis back to baseline values without affecting mean channel fluorescence. Reoxygenation reduced CD32w and CD16 expression with kinetics assays demonstrating concordance between reduced phagocytosis and CD32w and CD16 expression. Reoxygenation-induced decreases in CD32w and CD16 expression were prevented if whole blood PMN were incubated with either NaN3 (10 mM), dimethyl sulfoxide (DMSO) (10 mM), or taurine (15 mM) prior to reoxygenation. These results demonstrated that hypoxemia and hypoxemia/reoxygenation recruit and suppress distinct populations of whole blood PMN for phagocytosis. Intracellular kinase activation and Ca2+ mobilization are required for hypoxemia-induced increases in phagocytosis. Reoxygenation reduces whole blood PMN phagocytosis via an oxident-derived reduction of surface CD16 and CD32w expression.