Male aging is associated with alterations in plasma levels of antioxidants such as Coenzyme Q(10) (CoQ(10)) , and with a decrease of the fat-free body mass (FFM). In order to reveal, whether these changes can affect CoQ(10) metabolism, 73 non-obese, healthy males were studied, in age range 22-100 years, divided in 4 age groups: 20-55 (n = 23); 56-70 (n = 20); 71-90 (n = 8) and 91-100 (n =22). Serum CoQ(10) was measured by HPLC technique. Body composition was assessed by multifrequency bioimpedance analysis. Subjects aged 91-100 years displayed lower serum CoQ(10) levels and FFM than the other age-groups (p <0.001). Linear regression analysis revealed significant correlations between FFM and age (r = -0.82, p < 0.00001), serum CoQ(10) and age (r = -0.35, p <0.01). and serum CoQ(10) and FFM (r = -0.49, p < 0.001). Multiple regression analysis confirmed the correlation between serum CoQ(10) and FFM (p < 0.01), but did not for serum CoQ(10) and age. The proportion of FFM decreases with age. CoQ10 levels are also lower in older people, but they seem to be linked to FFM and not to aging itself. Since muscle tissue is the major component of FFM, and a reduction of the metabolic rate is another feature of aging, serum CoQ(10) may be an indirect index of metabolic activity in the elderly.