Recombinant human granulocyte colony-stimulating factor (rh G-CSF) enhanced resistance of mice against Listeria monocytogenes (LM) as determined by survival and bacterial growth. Mice pretreated with rh G-CSF twice daily for 5 days survived better than untreated animals to the challenge with LM. Number of bacteria in peritoneal cavity (PC) and spleen was lower in treated mice than that in the control group. Rh G-CSF increased mainly polymorphonuclear cells (PMN) in blood and spleen. After LM inoculation, a larger number of PMN and monocyte-macrophages accumulated in PC and spleen of tested mice. In addition, PMN primed in vivo with rh G-CSF released more superoxide anions when stimulated with phorbol myristate acetate. The inhibition of bacterial growth in PC and spleen could be ascribed to the accumulation of phagocytic cells at the infection sites and the increased oxidative metabolism. The results provided further evidence of the important contribution of G-CSF and neutrophils, as target cells, to the host defence against the intracellular bacteria.