This study was designed to examine whether concomitant administration of anti-free radicals with donorcore cooling on cardiopulmonary bypass (CPB) and hypothermic storage of the heart and lung, could provide successful extended cardiopulmonary preservation. Fourteen sheep heart-lung blocks harvested after core-cooling and cardioplegic arrest were preserved at 4 degrees C for 8.5 hr. Before and during CPB, the animals were perfused with Prostaglandin E1 (PGE1), superoxide dismutase (SOD), catalase (CAT) and deferoxamine (DEF). Cardioplegic arrest was induced with St. Thomas' Hospital solution (Plegisol) to which SOD, CAT and DEF had been added. The preservation solution consisted of Plegisol modified by the addition of K-lactobionate, raffinose, mannitol, SOD, CAT, DEF, a phosphate buffer and penicillin. Histological examination performed on 3 donor heart-lung blocks before and after CPB and cardioplegia, then immediately following cold storage, produced no clear evidence of structural damage in cardiac myocytes and lung parenchyma. Eleven donor organs were therefore transplanted in size-matched recipients with a total mean ischemic time of 12 hr. The combined administration of SOD, CAT, DEF, insulin and glucose during the initial period of reperfusion had no beneficial effect on cardiopulmonary performance. A progressive fall in Pa O2 and mean aortic pressure was observed post-operatively in the 7 animals that were weaned from CPB. Five of them died within 3 to 5 hr after CPB weaning, the remaining 2 animals died of cardiac arrest within the fourth hour. The results of this experiment seem to indicate that: 1. better organ function and improved survival could have been obtained if the duration of anti-radical treatment had been prolonged after reperfusion and, 2. physical manipulation of the donor grafts during harvesting and transplantation may have been partly responsible for the poor post-transplantation cardiopulmonary performance.