Oxygen free radical scavengers, such as superoxide dismutase (SOD) and catalase (CAT), have been shown to reduce effectively myocardial reperfusion injury. No such data have been reported for cold global pulmonary ischemia, which is required in heart-lung transplantation. Heterotopic heart-left lung allotransplantation was performed in 18 dogs after single-flush perfusion of the lungs with Euro-Collins solution (60 ml/kg), cardioplegic arrest, and 6 hours of cold global ischemia. Six dogs served as controls. In six other dogs prostacyclin (PGI2) was administered both into the pulmonary artery (20 ng/kg/min) and to the Euro-Collins solution (15 mg/L) before explantation (group A). Grafts in six other dogs were preserved with Euro-Collins solution plus SOD (40,000 U/L) and CAT (100,000 U/L)(group B). In addition, SOD (1 mg/kg) and CAT (1.5 mg/kg) were given intravenously during the first 20 minutes of reperfusion. There was no significant difference in cardiac output, right and left atrial pressures, nor pulmonary arteriolar resistance among the groups. In contrast, left atrial oxygen pressure (PO2) values were best in group B. At all times, PO2 values in animals in groups A and B exceeded those in control animals. Compared with control animals with Euro-Collins solution preservation alone, animals with both PGI2 and SOD/CAT preservation had significantly improved pulmonary function after heart-lung transplantation. Better oxygenation in the SOD/CAT group (group B) suggests an important impact of oxygen free radicals during reperfusion.