Alkali-soluble polysaccharides have been extracted from Laetiporus Sulphureus (Bull.: Fr.) Murr fruit bodies with a yield of 42.7%. The structure of the dominant polymer (16.05% of fruit bodies' mass), named latiglucan I, has been determined. It is linear beta-1,3-glucan (molecular weight 1.8 x 10(5) Da, [alpha]D-17 degrees).