Using a luminol-dependent chemiluminescence assay we found tert-butylhydroperoxide to be a strong inhibitor of respiratory burst of the mouse peritoneal macrophage. However, the protection against the inhibition of respiratory burst induced by tert-butylhydrope-roxide was enhanced after the intraperitoneal injection of polysaccharide from Coriolus versicolor. Further investigation exhibited that glutathione peroxidase activity was markly elevated in PSK-treated macrophages, Meanwhile, higher activity of glutathione peroxidase was maintained in PSK-treated macrophages incubated with tert-butylhydroperoxide. These results suggested that the immunological function of macrophage was related to the activity of glutathione peroxidase. Non-specific immunopolysaccharide might prevent macrophage from damage induced by reactive oxygen species by enhancing antioxidation capacity.