Between March 1970 and May 1976, 564 patients have undergone single or multiple heart valve replacement with the Hancock "SGP" bioprosthesis in our institution. Of these patients, 335 had single mitral, 102 aortic, one tricuspid, and 126 double or triple valve replacement, for a total of 629 xenografts. The long-term results, in terms of clinical improvement, survival, and complications, have been analyzed. Significant valve insufficiency secondary to primitive tissue alterations occurred in three patients, while reoperations were required in two for endocarditis and in two others for mitral stenosis caused by tissue ingrowth. We found that thromboembolic episodes occurred mainly in the early postoperative period up to the third month in 10 cases (1.76%). Three patients suffered peripheral embolization during the late follow-up period. Anticoagulants were not administered beyond 3 months postoperatively. Hemodynamic re-evaluation has been performed in 42 patients and the prosthesis has been shown to function properly either in the mitral or the aortic position. The data available to date indicate that the glutaraldehyde-preserved porcine valve is durable and we feel that its use is warranted in any valvular position.