Subset analysis of splenic lymphocytes using flow cytometry showed that the percentages of Thy1.2-(pan T-cells), L3T4-(CD4, helper T-cells), and Lyt2-(CD8, cytotoxic T-cells) positive cell populations were significantly increased in mice orally administered a hot water-soluble fraction from Agaricus blazei as compared with mice treated only with saline. 13C-NMR data indicates that the main component in the active polysaccharide is the complex of alpha-1,6- and alpha-1,4-glucan, which had already been shown to have anti-tumor activity against Sarcoma 180. It seems that the polysaccharide from Agaricus blazei may be an effective prophylactic, protecting humans against cancer by stimulating lymphocytes such as cytotoxic T-cells.