Estradiol and progesterone receptor proteins (ER, PgR) have been demonstrated in neoplastic and non-neoplastic human thyroid. The aim of this study was to determine the sexual steroid receptor content of pathological non-malignant thyroid (solitary adenoma, simple nontoxic goiter), and the adjacent normal tissue of the thyroid. The results show the presence of ER and PgR (cytosolic and/or nuclear) in most of examined tissues both pathological and normal. Low levels of steroid receptors are found in the cytosol fraction, whereas the receptor content is higher in the nuclear fraction. No correlation could be found between receptor levels and patients' age, menstrual state in females, and sexual steroid circulating hormones. A significant difference has been observed between adenomas and simple goiters (p less than 0.001) in the nuclear ER, and between normal tissue surrounding adenoma and normal tissue in goiters (p less than 0.05). This result suggests that estradiol and progesterone receptors are present in thyroid tissue and may have a physiological function.