The atrophic effects of two synthetic steroidal anti-androgens, chlormadinone acetate (CMA) and TZP-4238, on the adrenal gland of rats were investigated by histopathological and immunocytochemical procedures. Male Sprague-Dawley rats were divided into four experimental groups. Group 1 consisted of intact controls. Groups 2 and 3 received TZP-4238 10mg/kg/day and CMA 50mg/kg/day p. o., respectively, for 3 weeks. Group 4 received distilled water containing 2% Tween 80 instead of TZP-4238 or CMA. CMA caused marked atrophy of the adrenal gland. Histopathologically, the remarkable atrophy was observed in the adrenal cortical cells of zonae fasciculata and reticularis. Intracellular localization of glutathione-peroxidase (GSH-PO) which effectively reduces the lipid peroxides, was mainly observed in the cytoplasmic matrix (cytosol GSH-PO) near the mitochondria or lipid droplets. In ddition, immunoreactivity of intramitochondrial GSH-PO (mitochondrial GSH-PO) was less than that in the controls. Androgen receptor (AR) was localized exclusively in the nuclei of the adrenal cortical cells. In CMA-treated rats, AR was localized also in the nuclei of the adrenal cortical cells of the atrophic cortical zones. In contrast, TZP-4238 exerted no effect on the adrenal gland under the present experimental conditions. Therefore, it is suggested that TZP-4238 have a less inhibitory influence than CMA on the pituitary-adrenal axis. We further speculated that adrenal cortical cells of the atrophic zones induced by CMA treatment was decreased in corticosterone production and increased or remained in adrenal androgen production.