From June, 1971, through November, 1974, 75 patients underwent aortic valve replacement with a Hancock "Stabilized Glutaraldehyde Process" porcine xenograft. Patients who underwent multiple valve replacements are not included in the study. Thirty-nine per cent of the patients had procedures for associated lesions or for removal of a Starr-Edwards prosthesis. The operative mortality rate was 6.7 per cent. Six patients died in the late postoperative period. Only one death was thought to be secondary to a valve-related problem. Actuarial analysis predicts 84 per cent survival at 3 years. Three patients initially received long-term antithromboembolic therapy. There have been three suspected or documented thromboembolic episodes (0.24 per cent per patient-month). Ten per cent of the patients surviving the operation developed murmurs of aortic insufficiency. There have been no documented valve failures. Ninety-eight per cent of the survivors have experienced an improvement in their New York Heart Association (N.Y.H.A.) classification.