It has not been clear whether or not pulmonary ischemia-reperfusion injury would occur while ischemic lungs were maintained in a well-oxygenated state. Our aim was to develop an ischemic lung model whose oxygen tension was maintained and to determine whether or not ischemia without hypoxia would injure the lung. Rat lungs isolated, ventilated, and perfused with Krebs-Henseleit solution (0.04 ml/gm body weight) were obtained by a standard technique, and the left and right pulmonary arteries were isolated to enable selective perfusion to either lung. After the left lung was exposed to ischemia for 60 minutes with ventilation maintained by a normoxic (20% O2, 5% CO2, 75% N2; normoxia) or a hyperoxic (95% O2, 5% CO2; hyperoxia) gas mixture, it was reperfused for 30 minutes either in a forced way (occluding the right pulmonary artery for 10 minutes followed by perfusion of both lungs for another 20 minutes) or in the natural way (distribution of flow dependent on vascular resistance) to compose three experimental groups (forced reperfusion-normoxia, natural reperfusion-normoxia, and forced reperfusion-hyperoxia).(ABSTRACT TRUNCATED AT 250 WORDS)