If oxidative stress contributes to mitochondrial dysfunction, can mitochondrial dysfunction be reversed by changing the cellular oxidative status? A recent study attempted to answer this question using a transgenic mouse model to express human catalase targeted to the mitochondria (MCAT) [The following popper user interface control may not be accessible. Tab to the next button to revert the control to an accessible version.Destroy user interface control40]. Mitochondrial function was assessed both in vitro and in vivo in wildtype young (3–6 months old) and older (15–18 months old) lean healthy mice versus age-matched MCAT transgenic littermates. Whereas the older wildtype mice exhibited all the “usual” deleterious metabolic impairments including increased oxidative damage, reduced mitochondrial content (~30%) and function, increased intramuscular lipid (~70%), and marked muscle insulin resistance (~35%), the older MCAT mice resembled the young mice and demonstrated none of the age-associated impairments. These data suggest that by increasing ROS scavenging and reducing the oxidized state of the cell, many age-related deficits can be prevented.