Sex hormone receptors in human thyroid tissues. The behavior of sex hormone receptors was studied in the cytosol of thyroid tissue samples in order to clarify the effects of sex hormones on diseases of the thyroid. Androgen receptor (AR), estrogen receptor (ER), and progesterone receptor (PgR) were assayed using the dextran-coated charcoal (DCC) method and analyzed by the method of Scatchard. Androgen receptor, ER, and PgR were negative in all of the cytosol prepared from normal thyroid tissues. However, the positive rates for the receptors in the neoplastic and nonneoplastic tissues were 22% for AR, 29% for ER, and 18% for PgR. Especially, the incidence of ER was significantly higher in neoplastic lesions than normal tissues. These data suggest that sex hormones, especially estrogen, may play a role in diseases of the thyroid. 