Inhibin B is one of the growth factors mediating between Sertoli cells and germ cells. Inhibin B plays a role in the negative feedback control of FSH secretion in men. Inhibin B levels are low in the first week after birth in male newborns, then increase up to the 6th month of age and then decline progressively to reach their nadir towards 3-6 years. They become high again during puberty. Studies about influence of inhibin B on concentration and spermatogenic activity confirmed, that inhibin B can be used as a marker to estimate the Sertoli cells function. It has been proven that serum inhibin B levels in adult men correlate positively with sperm concentration. Inhibin B secretion decreases with men age what can be connected with FSH serum level increase. Inhibin B can be also used to diagnose and monitor many disturbances of spermatogenesis like different etiology azoospermia, primary testicular failure, hypogonadotropic hypogonadism, Kallman's syndrome, Klinefelter's syndrome, cryptorchidism, precocious puberty and complete or selective loss of subthalamus or pituitary function. Inhibin B is also considered as a good marker of spermatogenesis in population researches (especially together with FSH serum levels).