In vitro incubation of aminoglycoside antibiotics with human polymorphonuclear leukocytes (PMNs) has been shown to induce abnormalities in cell function. This study was designed to determine whether there are similar abnormalities in leukocyte function after exposure to the action of these agents in vivo. Four aminoglycosides (gentamicin, tobramycin, netilmicin, and amikacin) were tested. In vitro incubation did not induce a chemotactic defect when measured by an under-agarose method. However, inhibition of candidacidal activity was reproducible after in vitro incubation of all aminoglycosides tested. Nevertheless, when the aminoglycosides were administered intravenously to normal volunteers, PMN function, including adherence to nylon wool columns, chemotaxis, phagocytosis, and killing of Candida albicans, was unimpaired at 1, 3, and 24 h postinfusion. Therefore, we conclude that aminoglycoside antibiotic administration does not induce PMN dysfunction in vivo.