It is important to develop a sensitive assay method for evaluation of immunomodulating candidates including granulocyte-colony stimulating factor (G-CSF) which may augment host defense function against opportunistic infections. Effects of CSFs on anti-Candida activity of bone marrow cells (BMC) obtained from normal or cyclophosphamide-treated immunocompromised mice (CY-mice) were investigated. When BMC from CY-mice were preincubated for 24 hours in the presense of more than 0.005 ng/ml of G-CSF, anti-Candida activity was enhanced at 160 of effector (BMC) to target (C. albicans) ratio, whereas anti-Candida activity of BMC from CY-untreated mice was not changed at concentrations less than only by more than 0.5 ng/ml of G-CSF. Similar enhancement of activity was also observed in the presence of more than 0.05 ng/ml of granulocyte-macrophage colony stimulating factor (GM-CSF) in this assay using BMC from CY-mice. These findings suggest that this in vitro assay method can evaluate the activity of G-CSF and GM-CSF to augment leukocyte's anti-Candida activity.