The effect of leukocytes on the anti-Candida activity of neutrophils was examined. Murine neutrophils which were purified from casein-induced peritoneal cells inhibited the mycelial growth of Candida albicans. This anti-Candida activity of neutrophils was augmented by the addition of spleen cells prepared from mice pretreated with bacterial lipopolysaccharide 3hr before, but not from non-treated mice. The population in the spleen cells, which enhanced the anti-Candida activity of neutrophils, was plastic-plate adherent, nylon-fiber columns adherent and anti-Mac-1 antigen-positive. These immunological profiles suggested that the enhancing cells are classified to splenic macrophages. Peritoneal-exudated macrophages from mice treated with lipopolysaccharide also augmented the anti-Candida activity of neutrophils. These results suggest that the anti-Candida activity of neutrophils may be upregulated by activated macrophages.