The aims of the study were to determine the distribution of inhibin and its α subunit in some rat tissues by an immunohistochemical method of streptavidin-biotin complex (SABC) and to assess the transport mechanism of inhibin by investigating the localization of inhibin and α subunits in the central nervous system (mainly in hypothalamus and pituitary) of ovariectomized rats. Investigations on the extragonadal tissues of ovariectomized rats showed positive expression of inhibin and its α subunit in heart, kidney, spleen, pancreatic gland cells, but no positive reaction sites were seen in lung, liver, submaxillary gland, and adrenal gland. After injection with inhibin α subunit fragment or inhibin extract, positive reaction sites were observed in hypothalamus and pituitary of ovariectomized rats by SABC. Inhibin and its αsubunit was present in a wide variety of nonreproductive organs and tissues, and its expression was tissue specific, which indicated that inhibin might play a role in regulating tissue function through autocrine/paracrine mechanisms. Inhibin dimer and α subunit could be transported through the BBB by the method of "separation and reconstruction".