ABSTRACTThe Hindak strain of aCryptomonasspecies (Cryptophyceae) produces extracellular polysaccharides. Because there is no information on the structure of these compounds in the Cryptophyceae we conducted structural studies. Gas–liquid chromatographic analyses showed that the polysaccharide is composed of fucose, rhamnose, xylose, mannose, glucose, galactose, galacturonic acid, glucuronic acid, and traces of 3‐O‐methyl galactose. The polysaccharide was separated into two subtractions by ion‐exchange chromatography. Fraction A consisted mainly of 1,3‐linked galactose units and 1,4‐linked galacturonic acid. Unlike fraction B, fraction A did not have xylose, 3‐O‐methyl galactose, or glucuronic acid. Also, its degree of branching was low compared to that of fraction B. Only traces of sulfate were present infraction A, but fraction B was 10–15% sulfated. Protein was approximately 1% in both fractions. These polysaccharides appear to be a novel type of