Inhibin is a protein secreted by the Sertoli cells in men and by the granulosa cells in women. It inhibits the synthesis and release of the follicle-stimulating hormone in the pituitary gland and reduces the hypothalamic LH - releasing hormone content. It also inhibits the multiplication of spermatogonias in male gonads and the production of progesterone by the ovaries. Inhibin determinations in biological fluids may help to understand the pathophysiology of puberty, ovulation, menopause and various types of infertility.