Objective: To investigate the protective effect of ischemic preconditioning (IP) in the early phase of reperfusion injury. Design and methods: Control rat lungs were subjected to 3 h of perfusion, whereas the lungs of the ischemia-then-reperfusion (I/R) group were subjected to 2 h of cold ischemia following 30 min of perfusion. IP was performed by two cycles of 5-min ischemia followed by 5 min of reperfusion prior to 2-h cold ischemia. Results: Lipid peroxidation and antioxidant status were determined in tissue samples. Lipid peroxidation and reduced/oxidized glutathione (GSH/GSSG) ratio were increased; antioxidant enzyme activities were decreased in the I/R group whereas lipid peroxidation and GSH/GSSG ratio were decreased; antioxidant enzyme activities were increased in the IP group. Conclusion: IP appeared to have a protective effect against reactive oxygen species-mediated I/R injury in isolated rat lung. © 2005 The Canadian Society of Clinical Chemists. All rights reserved.