The effects of picolinic acid (PLA), a product of tryptophan catabolism, on anti-Candida activity of neutrophils were studied. Casein-induced peritoneal neutrophils of C3H/He mice partially inhibited mycelial growth of Candida albicans when cultured with C. albicans for 16h in vitro. The growth inhibition of Candida was augmented by a combination of neutrophils and more than 4mM picolinic acid. Especially in the presence of 200U/ml murine interferon-γ(IFN-γ), 2mM picolinic acid augmented the anti-Candida activity of neutrophils. The physiological significance of the augmenting effects of picolinic acid is discussed.