D-mannose, phophorus and potassium in a 5:1:1 ratio. The polymer is composed of 850 anhydromannose units. On the average every fourth anhydromannose unit is cross-linked through a fifth anhydromannose unit with a C(6) monopotassium phosphate group which is further bound in a diester linkage. The diester linkage is an α-(1,6')-linkage. The average molecular weight is about 157,000 .