Long-term variation (21-30 days) in the gonadotropic hormones level and testosterone was followed up in Klinefelter's syndrome (chromatine positive). Clinically, the authors followed up the development of the androgen-dependent target tissues before and after administration of 400 mg testosterone/month for 6 months. It was also found a fluctuation in the gonadotropic hormones secretion on a 21-30-day trial which differs from that of the normal adult male. We noticed a great variability of the androgen-dependent structures development in one and the same subject or in different subjects, and a low response to the action of big and prolonged doses of testosterone. The authors interpret these findings as a decrease in the sensitivity of the androgen-dependent target structures (hypothalamus and peripheral tissues) induced genetically and fundamenting the concept of the existence of a receptivity pathology.