Co-Enzyme Q10 (ubiquinone) is an important rate limiting cofactor in the mitochondrial electron transport chain, the biochemical pathway in cellular respiration from which adenosine triphosphate (ATP), the form of energy used by the body, is derived. Since cellular activities are dependent upon energy, co-enzyme Q10 is crucial for the efficient functioning of nearly every cell. In addition to its well-established function as a component of the mitochondrial electron transport chain, co-enzyme Q10 has in recent years acquired increasing attention regarding its antioxidant properties. Co-Enzyme Q10 occurs in all cellular membranes as well as in blood serum and in serum lipoproteins. As a lipid-soluble antioxidant, coenzyme Q10 efficiently protects membrane phospholipids and serum low-density lipoproteins from lipid peroxidation. And, as recent data indicate, it also protects mitochondrial membrane proteins and DNA from free radical induced oxidative damage.