A substance was isolated from the adrenal venous blood of dogs which is approx. 25 times as potent as DOCA in producing Na retention in adrenalectomized rats. It was not established with certainty that this substance is pure. The material is slightly less polar than cortisone, exhibits an absorption max. at 240 m[mu], does not react with the phenylhydrazine reagent descr. by Porter and Silber, and does not react with a phenylhydrazine reagent developed in this laboratory. The substance shows absorption maxima at 285 and 390 m[mu] when mixed with concentrated sulfuric acid.