Extracorporeal perfusion of isolated sheep lungs with blood after 30 min of ischemia caused injury manifested by polymorphonuclear (PMN) leukocyte sequestration, pulmonary hypertension, thromboxane release, and increased pulmonary vascular permeability. To determine the roles of ischemia, extracorporeal perfusion, and oxygen in this injury, lungs ventilated with 28% O2-5% CO2 and subjected to 30 min of ischemia followed by 180 min of perfusion (ischemic-perfused, n = 23) were compared with lungs subjected to (1) ischemia without perfusion (ischemic, n = 7), (2) perfusion without ischemia (perfused, n = 20), or (3) both ischemia and perfusion during ventilation with 95% N2 (anoxic ischemic-perfused, n = 15). Compared with ischemic-perfused lungs, ischemic lungs had an increased reflection coefficient for albumin (sigma alb, 0.82 +/- 0.03 versus 0.54 +/- 0.05) and decreased filtration coefficient (Kf, 0.05 +/- 0.01 versus 0.11 +/- 0.03 g.min-1.mm Hg-1.100 g-1). Perfused lungs had increased pulmonary hypertension, lung PMN leukocytes, and sigma alb (0.74 +/- 0.05); Kf was not different. Anoxic ischemic-perfused lungs had decreased pulmonary hypertension and thromboxane release, but sigma alb and Kf were not altered. These results suggest that extracorporeal perfusion caused PMN leukocyte sequestration, thromboxane release, and pulmonary hypertension, whereas ischemia caused derecruitment of vascular surface area. Injury required both ischemia and perfusion, but it was not decreased by anoxia, suggesting that oxygen radicals were not involved.