Recent studies have demonstrated that skeletal muscle cells are resistant to prolonged periods of ischaemia, but damage is observed after reperfusion. Periods of time longer than three hours of normothermal ischaemia in skeletal muscle lead to irreversible lesions. In the present study muscle metabolism during ischaemia and reperfusion was studied. After three hours of ischaemia two experimental groups were produced depending on whether or not they were to be followed by two hours of reperfusion. Adult mongrel dogs were submitted to ischaemia of the gracilis muscle. In this tissue, energetic metabolism was evaluated by its mitochondrial function and by glycogen level measurement. In a second experimental group the same ischaemic period was followed by two hours of reperfusion. The contralateral muscle of the same animal was used as a control. No changes in mitochondrial function, analysed by respiratory control ratio (RCR) or in any of its components, basal (state IV respiration) or ADP-activated (state III respiration) was observed. Glycogen levels also remained unaffected during the three hour ischaemic period and after two hours of reperfusion. We conclude that in the present dog model of gracilis preparation the skeletal muscle displays great resistance to ischaemia and reperfusion.