Objective: Lung injury induced by one-lung ventilation is rare, but it is acondition that may result in high mortality. This study evaluates the effects ofone-lung ventilation and occlusion time on collapsed and contralateral lungs.Methods: Sprague-Dawley rats were allocated randomly into 7 groups consisting of6 animals each: sham; O1, 1 hour of occlusion/2 hours of re-expansion; C1, 3 hoursof mechanical ventilation control; O2, 2 hours of occlusion/2 hours of re-expansion;C2, 4 hours of mechanical ventilation control; O3, 3 hours of occlusion/2 hours ofre-expansion; and C3, 5 hours of mechanical ventilation control groups. In theocclusion groups, the left lung was collapsed by bronchial occlusion. Malondialdehydeactivity was determined in the blood, and myeloperoxidase and malondialdehydeactivity was determined in the collapsed and contralateral lungs. Lung tissueswere also examined histopathologically.Results: Malondialdehyde and myeloperoxidase levels rose as occlusion durationincreased. This increase was greater in the occlusion groups than that in their owncontrol groups. Increases were significant in the O2 compared with the O1 groups(P .005). Histologically, tissue damage increased as occlusion time rose injury incollapsed and contralateral lungs. Injury was greater in the occlusion groups thaninjury in their own control groups (P .005).Conclusions: Our findings show that biochemical and histopathologic injury occurin collapsed and contralateral lungs in one-lung ventilation, and this injury increasesas occlusion time rises. We believe that occlusion and occlusion time-related injuryshould be borne in mind in the clinic under conditions requiring the application of one-lung ventilation.