The effect of low-dose aprotinin on hemostasis in patients undergoing cardiopulmonary bypass (CPB) for repeat valve replacement and coronary artery bypass operations were investigated. Thirty patients undergoing elective CPB from February 1993 through February 1995 at Catholic Medical Center were studied. the patients were randomly divided into two groups(15 patients per group) : group 1, receive 1, 000, 000 KIU/kg aprotinin in the CPB priming volume and 20, 000 KIU/kg aprotinin intravenously each hour during CPB ; group 2, without aprotinin administration served as the controls. The result showed that the early postoperative (during the first 24 hours) and mean postoperative total blood loss of the aprotinin group were significantly reduced than the control group (317.2 $pm$ 89.6ml in the aprotinin group versus 821.3 $pm$ 441.2rnl in the control group, p<0.01 ; 767.2 $pm$ 214.1 ml in the aprotinin group versus 1562.5 $pm$ 735.2 rnl in the control gorup, p<0.01). Total use of packed red ells and fresh frozen plasma was higher in control group(1.22 $pm$ 0.3 units versus 4.21 $pm$ 1.7units of packed red cells, p<0.01 : and 2.37 $pm$ 0.4units versus 6.72 $pm$ 0.88uni1s of fresh prozen plasma, p<0.05). We conclude the low-dose aprotinin was positive influence on postoperative blood loss in undergoing highly bleeding potency cardiac operation.