The synthetic vascular prostheses have been proved to be suitable substitutes for many parts of the arterial system. When these materials have been used to replace segments of the major veins, only moderate success has been achieved. It should be emphasized, however, that the reported successful synthetic venous grafts are largely limited to the intrathoracic vena cava.4 Similar experimental synthetic grafts of the infrarenal inferior vena cava have resulted in almost uniform thrombosis (Table 1). This marked difference in graft patency rates has not been completely explained. Various authors have attributed this to the negative intrathoracic pressure tending to hold the graft open while the positive intraabdominal pressure tends to occlude it. Also the low pressure, low-flow characteristics of the venous system appear likely to promote thrombosis in any less than ideal system. While it is not practical to achieve a negative intra-abdominal pressure, it is possible to modify