[Testosterone and infertility].

About 15% of men and women in their reproductive years remain childless; in 50% of cases the reasons can be found in the male partner. It is important to define as exactly as possible the reasons for infertility to select those men who can be treated by a causal treatment option and to find the optimum treatment strategy. While FSH is the key hormone for intact spermatogenesis, testosterone as an important modifier of quantitative normal sperm production may sometimes be underestimated. Exogenous substitution with testosterone will suppress spermatogenesis and is thus not indicated in hypogonadal males with hypogonadism and infertility at the same time. In males with normal to elevated gonadotrophins and symptomatic testosterone deficiency, treatment is difficult and evidence-based recommendations are missing. The situation in males presenting with secondary hypogonadotropic hypogonadism exhibiting one of the clearly defined and treatable reasons of male infertility is totally different. To stimulate the gonadal function in secondary hypogonadal patients wishing to father a child, pulsatile GnRH or subcutaneous gonadotrophin treatment are used. They stimulate both testosterone production and spermatogenesis. After the end of successful fertility treatment, substitution is continued by exogenous testosterone treatment with oral, transdermal or intramuscular physiological preparations.