Previously, we established an anti-androgen receptor (AR) monoclonal antibody. Using the antibody, we investigated immunohistological AR localization in human testes, epididymides, seminal vesicles and scrotal skins. The testes, epididymides and scrotal skins were obtained from a prostate cancer patient without pre-hormonal therapy undergoing bilateral orchiectomy. The seminal vesicles were obtained from a bladder cancer patient undergoing radical cystectomy. The tissues were immediately frozen in liquid nitrogen and kept at -80 degrees C until used. Cryostat-frozen sections were cut at 5 microns and stained by an indirect method. We obtained the following results. 1) In the testes, nuclei of Leydig cells were stained though Sertoli cells were not stained. AR localization in Leydig cells which produce testosterone suggests autocrine or intracrine mechanism in the testis. 2) In the epididymides, nuclei of epithelial cells of epididymal ducts were stained, while muscles and connective tissues were not stained. In the seminal vesicles, nuclei of glandular epithelial cells were stained. 3) In the scrotal skins, the cells of squamous cell layer have positive stainings. The cells in the upper portion of squamous cell layer were stained more intensely than the cells in the lower portion. The basal layer was not stained. The cells of the outer root sheath of hair follicles in the scrotal skins were also stained. 4) In androgen target organs, AR-positive cells and AR-negative cells were mixed in the epithelium of a glandular duct, which suggests heterogeneity of AR localization in the androgen target organs.