Between May, 1975, and May, 1979, 184 glutaraldehyde-preserved valve bioprostheses were implanted (92 aortic, 76 mitral, and 16 multiple). In the last two years, anticoagulants have been administered for the first three post-operative months. Of 176 patients, 10 patients had simultaneous coronary surgery, and five had previous valve surgery; endocarditis had occurred in eight patients before operation, and heart block existed in four patients. In the group of patients who underwent aortic valve replacements, there were four early deaths, all in patients with associated severe coronary artery disease. There was one late death in this group caused by bacterial endocarditis. In the group with mitral valve replacements, there were three early deaths, one related to massive thrombosis of the prosthesis, and two late deaths of unknown cause. Within the whole group, there were seven instances of significant thromboembolism, and nine instances of incompetence, including five mitral periprosthetic leaks which required reoperation. Three patients had stenosis of the mitral prosthesis. There has been no known incidence of intrinsic leaflet incompetence.