Changes of arterial and venous pressure, and cardiac output were studied following ligation of inferior vena cava below level of renal vein in dogs. Development of collateral circulation after ligation was followed by means of venography using Pyraceton. The following results were obtained. 1) Venous pressure rises six times as high as normal immediately after ligation and thereafter begings to decrease. The decrease of pressure is relatively rapid until one or two hours after ligation, and is retarded thereafter. Venous pressure still remaines one and a half time as high as normal even after 3 months. 2) Arterial pressure decreases about ten mm Hg following ligation of inferior vena cava and cardiac output decreases about 13 per cent, which are not marked in any respect. 3) Collateral circulation develops gradually after ligation and is almost completed three weeks later. Collateral vessels, which run apart from the point of ligation are established three weeks later. Recanalization at the point of ligation are noticeable four weeks later. 4) Vertebral plexus plays a significant role as a collateral circulation through all the course from beginning to the time of recanalization. 5) Moter disturbance of lower extremities and dilatation of veins on the lower abdominal wall are noted as sequelae after ligation. However, these phenomena are temporary and gradually subside.