Male sexual activity is in all mammalian species, included man, androgen-dependent. The role of testosterone (T) starts already during intrauterine life. It continues thereafter, inducing the development of sexual secondary characteristics and libido. Therefore T has represented the "classical" treatment of male sexual dysfunctions. In the therapeutic routinary use T is employed ad ester, like cipionate, enanthate and other i.m., undecanoate per os. When a pituitary defect is present and the testicular receptors are functioning a treatment with HCG can be employed.