Thyroid tissues, composed of normal thyroid (10 cases), Graves' thyroid (4), and papillary carcinoma (10), were measured for the presence of receptors for estrogen (ER) using an enzyme-immunoassay method. The mean value of ER in papillary carcinoma tissues (4.0 +/- 3.6 fmol/mg protein) was higher than that in normal thyroid tissues (0.8 +/- 0.4 fmol/mg protein) or that in Graves' thyroids (2.6 +/- 0.9 fmol/mg protein). In 10 papillary carcinomas, 3 were from male patients and 7 were from females. The mean value of ER in the tumors from male patients (7.2 +/- 5.1 fmol/mg protein) was higher than that from female patients (2.6 +/- 1.7 fmol/mg protein). Another set of 100 thyroid tissues from normal (20 cases), Graves' disease (10), follicular adenoma (8), and papillary carcinoma (62) was also examined for the presence of estradiol (E2) using an immunohistochemical method on formalin-fixed paraffin-embedded sections. E2-positive tissues were found in 4 (40%) of 10 Graves' thyroids, 4 (50%) of 8 adenomas, and 47 (76%) of 62 papillary carcinomas. In 62 papillary carcinomas, E2-positive tissues were found in 37 (73%) of 51 female patients and 10 (91%) of 11 male patients. In relation to relapse of the carcinomas, E2-positive carcinomas were found in 10 (71%) of 14 patients with relapse of the disease and in 14 (54%) of 26 patients with no relapse (the difference was not significant). The findings indicate that thyroid carcinomas may be estrogen-dependent, but no definite conclusions could be drawn between the biological behavior of the tumors and the E2-positivity.