In attempting to purify the specific part of the heterogenetic haptene, present in alcoholic extracts of horse kidneys, fractions were obtained which are distinguished from the common lipoids by their solubility in water. The material of one fraction described recently 3 is practically insoluble in alcohol, chloroform and ether and gives a viscous solution in hot water. With orcinol and copper it gives no purple color reaction in contrast to other water-soluble fractions; it contains neither phosphorous nor sulfur. It was possible to obtain from this serologically active product two fractions differing in their composition. The method of preparation was the following. The crude material separating from alcoholic extracts of horse kidneys and freed from ether soluble substances 1 was dissolved in 20 parts of hot pyridine and allowed to stand in the ice box for forty-eight hours. After removing the sediment the filtrate was evaporated under reduced pressure to nearly dryness.