Background: The protein complexes of the electron transport chain have been linked to the pathogenesis of diabetes mellitus (DM), but the interplay between DM and cytochrome c oxidase (complex IV) is not well understood. In this study, using a rat DM model, we evaluated the effect of DM on liver and kidney mitochondria, looking specifically at the characteristics of oxygen consumption by complex IV; we also studied the effects of DM on the protein composition of liver and kidney mitochondria.