Studies on the factors concerned in the production of hemorrhagic diathesis characterizing patients who have jaundice have been discussed in previous papers.1Numerous other investigators have demonstrated definitely that cholemic bleeding is caused by a deficiency of prothrombin in the circulating blood and that both this deficiency and the hemorrhagic state associated with it can be corrected by the administration of concentrates containing the fat-soluble antihemorrhagic vitamin K, together with bile salts to insure absorption of the vitamin. The early clinical application of this knowledge concerning vitamin K was begun independently in the United States by Warner and his associates2at the University of Iowa and by us, and abroad by Dam and his co-worker3in Copenhagen. During the past two years we have continued our observations on this problem, several lines of investigation having been pursued. We have endeavored to determine the reliability of vitamin K