['A postinjury immunodepression involving neutrophil functions has been described in critically ill patients. The aim of this prospective study was to search for a relationship between an impairment of neutrophil functions and the subsequent development of nosocomial infection.', 'Twenty-one severely ill (simplified acute physiology score II >20 on admission), nonimmunosuppressed patients who were receiving no antibiotics active against methicillin-resistant Staphylococcus aureus and highly resistant Pseudomonas aeruginosa were included. Twelve healthy subjects constituted a control group.', 'Neutrophil functions (phagocytosis and bactericidal activity toward S. aureus and P. aeruginosa in homologous plasma, reactive oxygen species secretion) were studied at day 4 +/- 1 after admission, and occurrence of nosocomial infection was prospectively recorded over the following 5 days. Interleukin-10 concentration was assessed by enzyme-linked immunosorbent assay. Results are expressed as median (25th-75th percentiles).', 'Six out of the 21 patients acquired a nosocomial infection during the 5 days after blood sampling (infected group). Compared with the patients who did not acquire nosocomial infection (noninfected group, n = 15), the neutrophils of the infected group demonstrated a higher percentage of intracellular bacterial survival (17% [2% to 67%] vs. infected: 62% [22% to 100%], p <.05), leading to an impairment of S. aureus killing in homologous plasma (killed bacteria: 4.93 log(10) colony forming units/mL [4.24-5.29] vs. infected: 3.62 log(10) colony forming units/mL [0.00-4.58], p <.05). Interleukin-10 plasma concentration was higher in infected patients (78 pg/mL [60-83]) compared with noninfected patients (22 pg/mL [14-58], p <.05). By contrast, P. aeruginosa killing was similar in patients whether or not they acquired a nosocomial infection.'] Does impairment of polymorphonuclear neutrophil functions precede nosocomial infections in critically ill patients?