Polymorphonuclear neutrophilic leukocytes (PMNLs) play a key role in host defense, and phagocyte dysfunction has been associated with increased susceptibility to infection in patients with thermal injury. We have used flow cytometric analysis (FCM) to longitudinally study PMNL expression of IgG Fc-receptor II (FcγRII) and Fc-receptor III (FcγRIII), as well as the complement receptors CR1 (receptor for C3b) and CR3 (receptor for C3bi) in 22 patients with large burns. Analyses of PMNL complement and immunoglobulin-mediated phagocytosis of Candida albicans were performed in parallel. Burn patient PMNL FcγRIII expression was decreased to 58% of control values at admission, and remained low for the first 3 weeks. The expression of patient PMNL FcγRII was not altered at admission or throughout the hospital stay. The CR1-dependent fluorescence was increased by 62% at admission, and reached a maximum at day 2, 138% greater than that of controls. The CR1 expression then gradually returned to normal at discharge. The PMNL CR3-dependent fluorescence showed an increase of 110% at admission and remained high during the first 3 weeks. The immunoglobulin-mediated phagocytosis was decreased by 12% at admission, whereas the lowest value was observed at day 10, with a reduction of 30% compared with controls. The patient PMNL complement-mediated phagocytosis of C. albicans was increased by about 160% at admission, and reached a maximum at day 2, before it gradually decreased to control levels at discharge. The expression of complement receptors correlated positively, whereas the expression of FcγRIII correlated negatively, with total body surface area (TBSA) burn. These results demonstrate significant changes of PMNL opsonin receptor expression and opsonophagocytosis, documenting strong systemic activation of PMNLs in the early phase after large burns.