Water-soluble extracts isolated from Hypsizigus marmoreus and fractionated by ion-exchange chromatography were investigated to determine their molecular characteristics and biological activities. The crude and fractionated water-soluble extracts (F(1), F(2) and F(3)) consisted mostly of carbohydrates (55.8-98.9%) with varied protein contents (1.1-23.0%). Their monosaccharide levels were significantly different, including the glucose content (67.0-100%) and galactose content (0-33.0%). The backbone of each fraction was mainly glucose molecules connected with 1,4-glycosidic linkages which contained considerable amounts of glucose and/or galactose connected through 1,6-glycosidic linkages. The average molecular weight (M(w)) of the extracts varied considerably, ranging from 1,665×10(4) to 19×10(4) g/mol. Little cytotoxicity was apparent in cancer cell lines from the addition of these extracts; however, they significantly stimulated Raw 264.7 cells to release nitric oxide (NO) and prostaglandin E(2) (PGE(2)), suggesting their potential immunomodulating activities.