Despite the widespread clinical use of polytetrafluoroethylene (PTFE) grafts, few reports dealing with their physical properties have appeared in the literature. In the past 20 months, 17 such grafts have been implanted into 15 patients threatened with limb loss, with an 88% immediate graft patency. Postoperatively, all patients underwent periodic evaluations; arteriograms were obtained in four. The effect of knee flexion on graft function was also studied. All grafts were found capable of withstanding cuff pressures in excess of 300 mm Hg without occlusion. With 90 degrees flexion, the grafts kinked crossing the knee joint but a pressure gradient or decrease in pulsatile blood flow did not develop. This remarkable resistance to external compression should render these grafts especially valuable for extra-anatomic bypass.