The influence on blood platelet aggregation of polysaccharides of mushrooms fractions obtained from Suillus luteus (SL-1, SL-2) and Trametes gibbosa (TG-1, TG-2) has been examined. All of the studied fractions show significant inhibition of aggregation, while TG-2 indicates the strongest effect. Because of complicated composition of polysaccharides fractions, the antiaggregation mechanism of their action is not clear.