Juvenile nasopharyngeal angiofibromas (JNA) are rare. They have been frequently treated with estrogens, either solely or as an adjuvant therapy prior to surgery or irradiation. Clinical trials have proveded no evidence to explain the objective respose to estrogens observed in some tumors. Since the mechanism of steroid hormone action is mediated via specific receptors, we analyzed 8 JNA for tumor cytosol estrogen receptors. None were positive for estrogen receptors. Additionally, all were also negative for progesterone receptors. Nasopharyngeal angiofibromas occur predominantly in adolescent boys at a time when there is a gradual change in androgen availability. Therefore, three latter angiofibromas were also analyzed for the presence of cytosol androgen receptor. Specific testosterone and dihydrotestosterone binding components in the tumor cytosol were detected. This observation raises for the first time the possibility that JNA may be an androgen-dependent tumor. Estrogen may act as an antiandrogen on these tumors, an action similar to that on prostate cancer.