Granulocyte colony-stimulating factor (G-CSF) stimulates a subset of granulocyte colony forming cells and when administered to neutropenic individuals results in recovery of blood neutrophil numbers to normal levels. Therefore, G-CSF may be a useful therapeutic agent for infections in immunocompromised hosts. However, to date there has been only limited information that G-CSF activates the antimicrobial activity of neutrophils. In the present study, we found that recombinant G-CSF promotes the anti-Candida albicans activity of normal human blood polymorphonuclear (PMN) cells in vitro using both a 3H-glucose uptake procedure and a Candida colony counting assay. As little as 0.1 ng/ml G-CSF induced significant anti-Candida activity in the PMN cultures. G-CSF treatment also enhanced superoxide anion production by the PMNs in response to f-MLP as determined by the superoxide dismutase inhibitable cytochrome C reduction method. Such results show that G-CSF can promote the antimicrobial activity of peripheral blood PMNs against C. albicans.