50 male healthy volunteers of different age had measurements of plasma luteinizing hormone (LH) and follicle-stimulating hormone (FSH). Basal levels of LH and FSH as well as maximal release of both hormones after i.v. application of 25 mug of synthetical LH-releasing hormone have been done. Results demonstrate an increasing reserve capacity of LH and FSH with age. FSH/LH ratio is altered in favor of FSH with duration of life. Sensitivity of gonadotropin producing cells of adenohypophysis to LH-releasing hormone is diminished in old age that can be recognized from a diminution of the relative rise of serum LH and FSH after LH-RH application. Correlations and partial correlations of absolute and relative body weight with age and basal LH and FSH serum levels demonstrate that age and not body weight plays a main part for increasing gonadotropin serum values. Causative responsibility for the increased LH serum concentrations is a decrease of testosterone production with age. Data obtained in this study and reports presented in literature give no convincing explanation for the increase of FSH serum levels with age.