Blood transfusions in open heart surgery become increasingly dangerous in recent years because of hepatitis and the AIDS virus. For this reason, blood saving methods must be considered when assessing the quality of cardiac surgery. To evaluate different blood saving methods, seventy two patients undergoing open heart surgery were divided into 3 groups. Aprotinin group(group I, n=35) and aprotinin with acute normovolemic hemodilution group (group II, n=15) were compared with prospective control group (group III, n=22). We administered the serine protease inhibitor aprotinin in high dosage(loading dose of 4mg/kg and maintaing dose of 1mg/kg/hr) to group I, and II patients. Acute normovolemic hemodiluation(ANH) was done before heparinization in group II. One to three units of blood could be withdrawn with a desired hematocrit of 30%. After an extracorporeal circulation (ECC), autologous transfusion was undertaken. Hematocrit, platelet count, and partial thromboplastin time(PTT) were measured immediately after induction, during bypass and at the intensive care unit. Amount of blood loss was measured in 12 and 24 hours after arrival at an intensive care unit. Amount of homologous transfusion was counted in postbypass period and 12 hours after arrival at an intensive care unit. Hematocrit was elevated in group II(p<0.05) after ECC Platelet counts were elevated and partial thromboplastin time was prolonged in group II in postbypass period and 12 hours after arrival at an intensive care unit compared with group I and III. Postoperative blood loss was 560.4±272.5cc in group I, and 282.0±98.6cc in group II, 819.3±428,0cc in group III. The use of homologus transfusion(packed red cells and fresh frozen plasma) in group I could be reduced by 49 & 66% and group II by 73 & 84% compared with group III. In conclusion our study suggests that administration of high-dose aprotinin is effective in reducing intraoperative and postoperative bleeding and therefore reduces transfusion requirement. In addition, combination of ANH and aprotinin can further reduce homologous blood usage.