In the 22 months from February, 1958, to December, 1959, a total of 55 Teflon arterial prostheses were inserted in femoral-popliteal bypass procedures at the Mayo Clinic without any hospital mortality. In an earlier paper<sup>4</sup>we reviewed our experience with homografts and Edwards-Tapp (ET) nylon prostheses and presented the early results from the first 23 Teflon prostheses. In this paper we shall present data on all Teflon prostheses inserted in femoral-artery bypass procedures to December 1, 1959, with special emphasis on factors contributing to failures. <h3>Indications for Operation</h3> Fifty-five prostheses were inserted in 44 patients. In 8 of the 44 patients prostheses were inserted bilaterally. Three patients had a second prosthesis on the same side for failure of the original prosthesis. The most common indication for bypass procedures was segmental occlusion of the superficial femoral artery as 41 prostheses, including bilateral prostheses in 7 patients, were inserted for this