In five patients who had massive, sudden, intraoperative hemorrhage, defined as loss of more than 1 L of blood in less than ten minutes, mean arterial pressure was initially maintained, and there were early increases in both systemic and pulmonary vascular resistance; however, cardiac output and oxygen delivery decreased. During control of hemorrhage and replacement of blood, wedge pressure and central venous pressure increased, and mean arterial pressure was maintained; however, cardiac output and oxygen delivery decreased, and oxygen consumption decreased below prehemorrhage levels. Three patients died postoperatively of multiple organ failure. The data indicate that anesthesia and operation affect both cardiopulmonary performance and peripheral oxygen transport, such that the ordinary physiologic response to hemorrhage are lessened. The absence of compensatory increase in oxygen consumption after resuscitation may have contributed to the high postoperative mortality.