Oxidative stress is involved both in metabolic syndrome and male infertility. Hypogonadism is also associated with increased risk for cardiovascular disease. To investigate the role of gonadal steroids in systemic antioxidant regulation, we determined plasma CoenzymeQ(10) (CoQ(10)) and total antioxidant capacity (TAC) in postsurgical hypopituitaric patients. Twenty-six patients aged 28-55 years were studied 6-12 months after surgery. CoQ(10) levels were measured by high-performance liquid chromatography and TAC by spectroscopy with the use of the mioglobin-H(2)O(2) system, which, in interacting with chromogen 2,2(I)-azinobis-(3-ethylbenzothiazoline-6-sulfonate), generates a radical after a latency time (LAG) that is proportional to antioxidant content. Sixteen patients presented low testosterone values; in 10 patients hypogonadism was isolated, and in 6 patients hypothyroidism also was present. CoQ(10) levels were significantly lower in isolated hypogonadism than in normogonadism. Testosterone treatment, performed in those patients with isolated hypogonadism, induced a significant enhancement both in CoQ(10) level and LAG. CoQ(10) and LAG values correlated significantly, suggesting an interrelationship between different antioxidants. Our data suggest that hypogonadism could represent a condition of oxidative stress, in turn related with augmented cardiovascular risk.