The importance of the quality of elasticity in a plastic arterial prosthesis is being generally recognized. While in some anatomical locations, and with rather strict limitations on the length of the segments to be replaced, rigid prostheses may perform well, from the viewpoint of wide-range usefulness the ability to elongate and flex without deformity is an essential characteristic of arterial substitutes. As abundantly proved by both clinical and experimental1 evidence, without this quality a plastic arterial implant will buckle whenever the anatomical circumstances require bending, and the result of buckling is almost invariably thrombosis. We have formerly described2 a plastic tube partly composed of specially processed ("Helanca") nylon yarn, which possessed the quality of stretchability. Unfortunately, in experimental studies, while yielding excellent patency rates, the stretch-nylon prosthesis disclosed unsatisfactory durability. More recently a prosthesis of similar construction, but made of Dacron * yarn, has been developed and has given very