A review. Coenzyme Q10 (Q10) is an important component in bioenergetic processes of mitochondria in the cells of human tissues, especially in the mitochondrial respiratory chain. It serves as a carrier of electrons from flavin to the cytochrome system. It also was suggested that Q10 may act as an antioxidant. Low coenzyme Q10 concentrations in human blood or tissues were discussed in relation to heart diseases, hypertension, neurol. disorders, diabetes, and cancer. Interactions between 3-hydroxy-3-methyl-glutaryl-CoA reductase inhibitors (statins) and Q10 may be of significant importance, since the biosynthesis of cholesterol as well as Q10 involves a series of identical enzymic reactions and statins seem to impair the synthesis of Q10. The supplementation of Q10 has minimal side effects and his efficacy was demonstrated in different clin. disorders.