Abundant evidence is now available that administration of vitamin K to vitamin K-deficient chicks and to bile fistula animals leads to an increase in the prothrombin level and a decreased clotting time of the blood. Administration of deoxycholic acid is necessary to insure absorption of the antihemorrhagic factor when it is given orally to bile fistula animals. It was suggested by one of us that, since vitamin K combines with deoxycholic acid, possibly the best method of administering this vitamin orally would be in the form of the choleic acid. This compound has recently been prepared by Almquist and Klose. They showed that oral administration of the choleic acid to vitamin K-deficient chicks leads to a decrease in the clotting time of the blood. The present experiments indicate that oral administration of this choleic acid to bile fistula rats is followed by an increase in the prothrombin level of the blood. The choleic acid was kindly supplied to us by Dr. Almquist. It was fed in varying levels to choledochocolonostomized rats. The data are given in Table I. Although the oral administration of the choleic acid of vitamin K led to an increase in the prothrombin value of all of the bile fistula rats, the prothrombin values are below normal. It may be necessary to give larger doses in order to increase the prothrombin levels further. Experiments to determine the optimum dose of the choleic acid are in progress.