Intraoperative autotransfusion was studied in 62 patients undergoing elective or emergency thoracic or abdominal vascular surgery systemic heparinization. The results in 58 patients who received a mean autotransfusion volume of 1.8 liters were compared with a group of four patients in whom 9 liters of blood was autotransfused. The quality of the autotransfused blood also was studied and was shown to have a normal platelet count (mean, 144,000/cu mm) and normal fibrinogen value (mean, 212 mg%). No significant differences in the hematological or coagulation parameters measured were detected in the groups given moderate or massive autotransfusion. The mean homologous blood requirement during the hospital admission in the "moderate" group was 300 ml and in the "massive" group 1,000 ml. With careful technique excessive hemolysis or pulmonary microaggregate embolism does not occur; 75% of patients required no homologous blood throughout their hospital admission. No complications which would be attributed to autotransfusion were seen in either group. It is concluded that intraoperative autotransfusion is safe and effective and deserves wider application.