MitoPBN is a mitochondria-targeted antioxidant. It accumulates in the mitochondria following the generation of a mitochondrial membrane potential by succinate, an effect that is blocked by addition of the mitochondrial membrane potential uncoupler FCCP . MitoPBN inhibits superoxide activation of mitochondrial uncoupling protein 1 (UCP1), UCP2, and UCP3 when used at a concentration of 250 nM in vitro but does not react with superoxide. It traps hydroxyl (IC50 = ~77 μM) and carbon-centered radicals and inhibits the initiation of lipid peroxidation in isolated bovine heart mitochondria.