The feasibility of replacing the canine inferior vena cava with autogenous peritoneal tubes, dacron grafts and autogenous aorta was assessed. In another group of dogs a portion of the inferior vena cava was divided and anastomosed as a control. Regardless of the type of graft employed, thrombosis universally occurred within four months. No graft demonstrated clear superiority over the others. Thrombosis of the grafts appears to be due to occlusion by perivascular scar tissue. The factors of venous flow and pressure appear to be of more significance in determining continued patency of a venous graft than the type of graft employed.