In this study, administration of carnitine and alpha-lipoic acid to aged rats was found to increase skeletal muscle mitochondrial respiration, and in turn, increase the level of ATP. The study involved both young (3-4 months) and aged (over 24 months) rats. Measurements of mitochondrial membrane swelling and mitochondrial respiration (states 3 and 4) found that aged rats had an increased mitochondrial membrane swelling and state 4 respiration, whereas they had a decreased state 3 respiration, respiratory control ratio (RCR) and ADP:O ratio, compared with young rats. After administration of a combination of carnitine and alpha-lipoic acid for a period of 30 days, the condition of the aged rats improved. Specifically, mitochondrial membrane swelling and state 4 respiration returned to near normal levels, while the state 3 respiration and RCR increased. The results of this study suggest that the combination of carnitine and alpha-lipoic acid may have potential as a treatment for mitochondrial damage associated with aging.