In previous communications from the staff of the Massachusetts General Hospital we have indicated that we are confronted with a serious problem concerning venous thrombosis with resulting pulmonary embolism. Hampton and Castleman1have shown that infarcts to the lungs are easily interpreted by roentgenographic studies. Many of the postoperative pulmonary sequelae, previously attributed to other causes, are embolic in origin. Castleman,2from autopsy studies, has found the source of pulmonary embolus in our clinic to be from the deep veins of the legs in approximately 95 per cent of the cases. Miller and Rogers3in earlier studies recognized the importance of this syndrome in our clinic. Data collected by Davis4prior to 1925 showed that 3 patients in each thousand subjected to major surgical procedures succumbed to pulmonary embolism. Methods to prevent venous stasis by posture, combined with early passive and active exercise, reduced the incidence