The free radical theory of the aging process is based on the hypothesis that with increasing age, mutations of the mitochondrial DNA will accumulate and will at least lead to a loss of function with subsequent acceleration of cell death. Even if this theory is widely accepted, the reactive-oxygen-species-induced mutations of mitochondrial DNA, the accumulation of mitochondrial DNA and the role of antioxidants are not fully understood. Based on this theory, supplements with unproven mixtures of antioxidants or hormones, such as melatonin with antioxidant properties, are widely recommended and cover a big market. However, we are far away from understanding their specific role and we have to consider that, based on the free radical theory of aging, the balance of antioxidants and prooxidants in both directions is of importance in maintaining the physiological function of both reactive oxygen species and antioxidants.