Despite blood conservation techniques, the average transfusion requirement in patients undergoing elective cardiac surgical procedures remains 1 to 3 units. We studied the efficacy of predonated autologous blood in decreasing homologous transfusion in two matched groups of 58 patients each. Group 1 received homologous blood perioperatively, and Group 2 was transfused with predonated autologous blood. An average of 1.97 units was predonated in Group 2 over 18 days. This resulted in a decline in whole blood hemoglobin concentration of 2.2 gm/dl. No complications resulted from phlebotomy in this ambulatory population consisting predominantly of patients with coronary artery disease. Transfusion of an average of 1.7 units of autologous blood in Group 2 reduced the volume of homologous transfusion by 46% compared with Group 1 (p less than .01). In Group 1, 38% of patients required no homologous transfusion compared with 64% in Group 2 (p less than .02). There were no complications related to autologous blood transfusion. Total transfusion requirement was related to the length of cardiopulmonary bypass. We conclude that autologous predonation is a simple, safe, and cost-effective method of reducing homologous transfusion and thereby decreasing the risk of transfusion-related reactions and infections.