A novel polysaccharide Fraction K-2-F containning 3-O-methylgalactose, which was isolated from the 70% aqueous ethanol extract of the fruiting body of Phellinus robustus Karst., was found to be homogeneous as judged by gel filtration on Sepharose CL-4B, and its molecular weight was estimated to be ca. 470,000. Another low-molecular polysaccharide fraction (K-2-L) obtained from the same extract was composed of a large amount of glucose (ca. 83%) in addition to mannose, 3-O-methylgalactose, and galactose. K-2-L showed a characteristic absorption band at 890 cm^ in the infrared spectrum, suggesting the presence of β-glycosidic linkages. In biological screening tests, K-2-F and K-2-L exhibited mitogenic activity in a dose-dependent manner, and the mitogenic potency of K-2-F was stronger than that of K-2-L. In addition, only K-2-F showed significant colony-stimulating factor-inducing activity
