To evaluate the protective effect of continuous pulmonary perfusion with oxygenated blood during aortic crossclamping, 12 mixed-breed piglets (7-12 kg) were placed on cardiopulmonary bypass for 130 minutes. An experiment group of 6 (group E) had continuous pulmonary perfusion with oxygenated blood during cardiopulmonary bypass, while the other 6 served as controls (group C). Pulmonary function was measured at the beginning and end of cardiopulmonary bypass and one hour later. Histology was compared before and after cardiopulmonary bypass. Pulmonary function after cardiopulmonary bypass was significantly better in group E than group C. There was preservation of the normal pulmonary parenchyma in group E, whereas group C had marked intra-alveolar edema and abundant intra-alveolar neutrophils. Anoxia of lung tissue during aortic crossclamping on cardiopulmonary bypass is probably the major factor in lung injury. Continuous pulmonary perfusion was effective in preventing lung injury during aortic crossclamping.