Since 1937, when A. J. Quick demonstrated the relation of a low prothrombin level in the blood to a hemorrhagic tendency, there has been application of the Quick prothrombin test in the investigation of the bleeding tendency in many clinical entities. It has been established that a definite prothrombin deficiency is associated with the bleeding observed in obstructive and catarrhal jaundice.1 A prothrombin deficiency has been observed in hemorrhagic disease of the newborn and in other clinical conditions, as has been well summarized by Snell and Butt.2 In a certain number of cases pulmonary tuberculosis is complicated with hemorrhage. This symptom of hemoptysis is most harassing and alarming to the patient. The incidence has been reported as ranging from 20 to 80 per cent. A. R. Masten3 found that 33.8 per cent of 1,000 patients admitted to a sanatorium because of pulmonary tuberculosis had hemoptysis before discharge