The term hemorrhagic disease of the newborn was introduced by Townsend1in 1894 to include a variety of bleeding disorders which occur during this period of infancy unrelated to trauma, infection, or definite disease. The condition was differentiated from hemophilia. In 1910 Schwarz and Ottenberg2reported a prolonged coagulation time in these cases, and two years later Whipple3advanced the hypothesis that the condition was due to a lack of prothrombin. Very low values of this factor were reported by Gelston4and later by Kugelmass et al.,5but in these studies very inaccurate methods were employed. In 1937 Brinkhous, Smith, and Warner6with a two-stage technique showed that the defect of coagulation of normal newborn infants was due to a reduction of blood prothrombin. After this, independent publications from different parts of the world established the value of vitamin K in prophylaxis and treatment