In comparison with saphenous vein bypass grafting (SVG) without a pleurotomy, internal mammary artery (IMA) bypass surgery might enhance more blood loss by the intrathoracic wound and a wide opened pleura. Low-dose aprotinin (Trasylol) reduces blood loss and consequently, the use of homologous blood. We studied the blood loss and blood requirements peri-operatively in 70 patients, who underwent either SVG-(n = 35) or IMA-surgery (n = 35) without aprotinin and another 70 patients who underwent SVG- (n = 35) or IMA-surgery (n = 35) with a single dose of aprotinin, added to the pump prime. We also determined the hemoglobin and total protein content of the shed blood. Without aprotinin administration, the mean intra-operative and post-operative blood loss was significantly less (p < 0.01) in SVG-patients, than in IMA-patients. We observed no statistical differences in the mean blood requirements between SVG- and IMA-surgery (1.2 units and 1.6 units). The use of any homologous blood product was similarly averted in 39% of the SVG-patients, and in 48% of the IMA-patients. Treatment with aprotinin significantly lessened (p < 0.01) the mean intra-operative blood loss only in IMA-patients. Post-operative blood loss was diminished with 45% in IMA-patients and 33% in SVG-patients, being significantly less (p < 0.01) after SVG, than after IMA-surgery. Blood requirements were significantly lowered (p < 0.01): a total mean of 0.2 units in SVG- and 0.6 units in IMA-patients (NS). Any homologous blood product was prevented in 78% of the IMA-patients and in 87% of the SVG-patients (NS). The mean loss of hemoglobin and total protein per 100 ml of shed blood was similar in IMA-, and SVG-patients with or without aprotinin, although aprotinin diminished the total amounts in both groups with 50% (p < 0.01).