We investigated the immunohistochemical localization of androgen receptor (AR) using a polyclonal antibody for 55 KD recombinant human AR in human tissues fixed with 4% paraformaldehyde solution and embedded in paraffin. Immunoreactive AR was restricted to the nuclei of various tissues. Among the well-known androgen target organs, secretory cells and basal cells of the prostate, spermatogonia, spermatocytes, Sertoli cells and Leydig cells of the testis, epithelial cells of the rete testis, fibroblasts in the whole organ, squamous cells, sweat gland and hair follicle cells of the skin, and hepatocytes of the liver were positive for AR. In addition, smooth muscle cells of the prostate, uterus, urinary bladder, gastrointestinal tract, arteries, and arterioles were strongly immunoreactive for AR. Cardiac muscle and striated muscle of psoas were positive for AR. Acinar cells, ductal cells, and myoepithelial cells of the breast, endocervical and endometrial cells of the uterus, cyto- and syncytiotrophoblast of the chorionic villi, and tubules of the kidney were also positive for AR. Most FSH, LH, and some GH endocrine cells in the anterior and posterior lobes of the pituitary gland, follicular cells of the thyroid gland, and adrenocortical cells were positive for AR. Cells immunoreactive for AR were ubiquitously distributed throughout the entire body. The present study demonstrated the diversity of androgen effects on many target tissues.