The pathogenesis of thyroid cancer is complex. Iodium deficiency, genetic factors, sex, older age, irradiation in childhood, thyroid growth stimulating antibodies and epithelial growth factor possibly affect its development. Recent reports, also epidemiological, have shown that differentiated thyroid cancer (papillary, follicular, oxyphillic) is dependent on sex hormones, especially estrogens. This has prompted research into the presence of estrogens and progesterone, as well as androgen receptors (ER, PR and AR) in normal and neoplastic thyreocytes and estradiol content in thyroid tissue. The results of these investigations imply that thyroid cancers are estrogen-dependent. There is, however, no agreement in reports about correlation between tumor malignancy and ER, PR and AR expression. In this study 72 thyroid glands have been examined using immunohistochemical assays with ERs and PRs antibodies. Positive staining was demonstrated mainly in differentiated thyroid cancer nuclei (17 ERs positive and 2 PRs positive). There was no expression of antibodies in non-neoplastic cells or in adjacent tissues. The nuclei of 3 oxyphillic and 4 follicular adenomas were also ERs positive. On the other hand nuclei of 5 follicular adenomas were PRs positive. These results are in agreement with most available data. It seems, however, that the material so far examined by the investigators is too small. Furthermore, because of using various methods the results cannot be compared. Further studies are necessary to reveal if there is any true influence of sex hormones on the development of thyroid lesions and if the detection of sex hormone receptors may help in choosing adequate therapy.