The purpose of this study was to evaluate the effect of aprotinin on intraoperative bleeding and graft patency in 200 patients undergoing elective CABG. Patients were classified into three groups; patients receiving 1500000 KIU of aprotinin (group A), 300000 KIU of aprotinin (group B) and no aprotinin as the control (group C). The groups were almost the same as to age, sex, number of grafts and use of ITA. Intraoperative bleeding and reexploration were significantly decreased in group A compared with group B and C. All patients underwent coronary angiography between the 4th and 8th post-operative weeks. Graft patency was significantly decreased in group A (SVG: 90.4%, ITA: 91.1%) compared with group B (SVG: 95.3%, ITA: 100%) and C (SVG: 95.5%, ITA: 99.2%). Perioperative myocardial infarction increased in group A (3.7%). Aprotinin was effective in reducing intraoperative bleeding in CABG, but decreased early graft patency after CABG. It is suggested that aprotinin should not be used routinely in CABG unless a patient has bleeding tendency which is likely to be seen in emergency and redo surgery.