Two 3-m2 Landé-Edwards membrane oxygenators were linked in parallel and joined with a standard roller pump apparatus for total cardiopulmonary support during aortocoronary artery-vein bypass operations. Three 3-m2 membranes were used for patients weighing over 80 kg. Normal levels of oxygen, carbon dioxide and arterial pH were obtained when the membrane was used properly. Satisfactory platelet counts over 800,000/ml and plasma hemoglobin levels below 50–100 mg°/o documented the safe levels of blood destruction. Better postoperative pulmonary and cerebral function was noted after membrane support than with the use of the bubble oxygenator support. 12 consecutive patients, 41–103 kg, had successful partial and total cardiopulmonary support during elective aortocoronary artery-vein graft operations lasting 1 to 6.5 h. Prolonged pump runs were made when previous operations had produced pericardial adhesions, when multiple vein grafts were needed or when low cardiac output dictated cardiopulmonary support before beginning the oper