Inhibins and activins are dimeric glycoproteins, member of the transforming growth factor beta (TGF beta) superfamily. The main source and targets of inhibins during the fertile age, in non pregnant women, are the ovaries, while during pregnancy placental production becomes predominant. Activin is produced from several organs: brain, ovary, uterus, placenta and spleen. During the menstrual cycles, inhibin B concentrations rise in the follicular phase with a peak after the ovulation peak of LH, inhibin A becomes predominant in the luteal phase. During reproductive life no significant change of activin A serum concentrations have been demonstrated. Inhibins and activins play an important biological role in the regulation of the HPO axis. The evaluation of inhibins and activins change is useful in understanding the pathophysiology of gynecological diseases and in the diagnosis of obstetric and gynecological pathologies.