Topical cooling of the lung was compared with cold crystalloid pulmonary artery perfusion with modified Euro-Collins solution in a canine model of unilateral left lung allotransplantation with ligation of the recipient's contralateral pulmonary artery and main bronchus. Lung preservation for 6 hours was achieved by topical cooling and storage at 4° C after absorption atelectasis in five dogs and in a further five dogs by pulmonary arterial perfusion of Euro-Collins solution; 60 ml/kg at 4° C, modified with MgSO4 6 mmol/L followed by storage at 4° C. Dogs in the perfusion group were pretreated with an infusion of the synthetic analog of prostaglandin I2, iloprost (20 ng/kg/min). The ischemic times were 5.97 hours ± 0.09 for the topical cooling group and 5.96 hours ± 0.04 for the perfusion group. After transplantation, artificial ventilation at a fixed oxygen concentration was continued until the recipient's death or elective termination of the experiment at 24 hours. Assessment of pulmonary preservation was by animal survival, blood gas analyses, and measurement of lung weight and water in the transplanted lung. No animal in the topical cooling group survived more than 5.5 hours after transplantation; all perfusion recipients survived 24 hours. Oxygenation in the topical cooling group was significantly reduced 1 hour after contralateral ligation: Oxygen tension was 224.2 mm Hg ± 5.8 before ligation and 92.6 mm Hg ± 22.3 after ligation (p < 0.001). There was no significant change in oxygenation in the perfusion group 1 hour after contralateral ligation: Oxygen tension was 219.2 mm Hg ± 9.1 before ligation and 207.9 mm Hg ± 10 after ligation (p = not significant). A highly significant difference in oxygen tension measured at 1 hour after contralateral ligation was present between the two groups: topical cooling 92.6 mm Hg ± 22.3, perfusion 207.9 mm Hg ± 10 (p < 0.001). Mean lung weights in the topical cooling group were significantly higher than those in the perfusion group: topical cooling 168.3 gm ± 20.8, perfusion 82.9 gm ± 5 (p < 0.01). Total lung water content was significantly increased in the topical cooling group: topical cooling 12.29 ml/kg ± 1.39, perfusion 4.14 ml/kg ± 0.06 (p < 0.001). These data suggest that topical cooling alone does not achieve optimal lung preservation for transplantation, but that lungs may be successfully preserved for 6 hours with cold crystalloid pulmonary perfusion.