Partially purified polysaccharides were obtained from four medicinal mushroom species, Agaricus bisporus, Agaricus brasiliensis, Phellinus linteus and Ganoderma lucidum by hot water extraction, followed by ethanol precipitation. The four samples contained varying amounts of both a- and ß-glucans as determined by FT-IR and by quantitative estimation after prior partial hydrolysis (Megazyme ß-glucan assay kit). EC50 values of the DPPHradical dot scavenging activity of the polysaccharides from G. lucidum spores and P. linteus fruiting bodies were found to be particularly low, i.e. EC50 <0.1 mg/ml. For A. brasiliensis and A. bisporus, EC50 values were 0.27 and 2.0 mg/ml. EC50 values of the antioxidant activity were 7.07 mg/ml for G. lucidum, 13.25 mg/ml for A. brasiliensis and >20 mg/ml for A. bisporus polysaccharide, respectively. EC50 values of the chelating activity of ferrous ions ranged from 0.59 mg/ml for G. lucidum to 7.80 mg/ml for A. bisporus. The EC50 values of the extracts in the reducing power assay ranged from 0.47 to 14.83 mg/ml. A correlation was found between EC50 values of the chelating and reducing power abilities and the amount of total glucans content in the extracts. In vitro measurements of immunomodulatory capacity of polysaccharide extracts showed that A. bisporus, A. brasiliensis fruiting bodies and G. lucidum spores extracts express an immunostimulating effect on activated human PBMCs and induce synthesis of IFN-¿. The polysaccharide extract of P. linteus fruiting bodies showed an immunosuppressive effect.