Inhibin A and B is defined by its endocrine activity in suppressing follicle stimulating hormone (FSH) secretion by the pittútary and by pituitary cells in culture. Bioactive Inhibin is a heterodimeric glycoprotein composed of the a subunit and one of two possible R subunits, (3A or (3B, connected by disulphide bridge. Human body fluids contain forms of free a subunit not associated with any R subunit and lacking Inhibin bioactivity. The synthesis and secretion of dimeric Inhibin A and B are confined to the reproductive system (ovary, testes and foetoplacental unit). Some tissues make either ohly activins (no synthesis of a subunit) or oraly free Inhibin a subunit (no R subunit). Inhibin circtdates ira human serum complexed to aZ-macroglobulin, which has a low affinity. Both the strukture and expression of a membrane components of the Inhibin receptor system and a model of the mechanistu of Inhibin action ira target cells has been described. Inhibin is a member of the transforming growth factor R (TGF R) superfamfly, the group of structurally similar but functionally diverse growth factors and has local paracrine actions ira the gonads. Inhibin is a new marker of gonadal function both ira man and women and appears to be important for the use ira clinical practice.

        Key words: Inhibin, strukture, FHS, receptor system, physiological endocrine and paracrine functions