Juvenile nasopharyngeal angiofibromas, which occur predominantly in adolescent males, are frequently treated with estrogen in an effort to decrease the size and vascularity of tumors prior to surgery. If has been presumed that the tumors may have close relations to the sex hormones. However, the mechanism of hormonal action has not been completely known and the presence of sex hormone receptors has not been proved too. We studied for the presence of the estrogen and progesterone receptors of 11 cases of the nasopharyngeal angiofibroma by immunohistochemical method using the monoclonal antibodies to estrogen and progesterone receptor. In the present study, 4 out of 11 cases(36%), 3 cases in endothelial cells of vessel wall, 1 case in fibroblasts of stroma, were positive to the estrogen receptor, However, none was positive to the progesterone receptor. The inferior turbinate tissues in 5 normal adolescent males as a control group revealed all negative reactivity to estrogen and progesterone receptor. From above results, authors concluded that the estrogen may have some direct effect on tumor growth and blood vessel wall in some cases following estrogen administration.