Early and late experience with 1,000 patients undergoing porcine xenograft replacement of cardiac valves from 1974 through 1981 at Emory University Hospital is presented. Hemodynamic performance of the modified orifice Hancock and the Carpentier-Edwards valves has been quite satisfactory. There has been a low incidence of thromboembolism in the absence of routine anticoagulation. Less than 20 per cent of our patients are anticoagulated long-term, the primary indication being chronic artrial fibrillation. Endocarditis has developed in 0.7 per cent of patients, an incidence comparing most favorably with that of mechanical prostheses. Valve dysfunction secondary to primary tissue failure is a definite problem. The highest incidence of tissue failure occurred in young patients after six years of implantation. Detailed analysis of long-term patient survival showed a low incidence of valve related deaths. The porcine xenograft is a satisfactory prosthesis for cardiac valve replacement. Our data suggests its use should be limited to older patients or to patients in whom anticoagulation is contraindicated. It should be explained to all patients that long-term durability is unknown and that re-replacement of these bioprostheses within a decade is quite likely.