Aim In order to find out the effect of polysaccharide krestin(PSK) on nitric oxide (NO) production in mouse peritoneal macrophages. Methods The content of NO in cell cultures was analyzed by a method using Griess reagent, and the cell number was determined by staining with crystal violet. Results Without any stimulation,there was no alteration of NO production in mouse peritoneal macrophages by PSK primed, but when the cells were stimulated with lipopolysaccharide (LPS), NO production increased greatly(P< 0.01 ); furthermore, NO production didn’t change when the PSK primed macrophages were incubated with interferon γ (IFN γ). Conclusion PSK could regulate NO production in macrophages; and the effect of PSK was somewhat like that of IFN γ. The relationship between the effects of PSK and IFN γ needs to be further uncovered. 还原