We describe the distribution of interleukin-6 and interleukin-1α in thyroid tissues obtained from patients with autoimmune diseases or neoplastic thyroid disorders employing immunohistochemistry in sections from paraffin embedded tissue blocks. Interleukin-6 was found in thyroid follicular epithelial cells (TFEC) from papillary carcinomas (four of five patients) but not in follicular carcinomas (five patients). Interleukin-6 was also detected in non-toxic multinodular goiters (four of seven patients), in patients with Graves' disease who did not have an early recurrence of hyperthyroidism after surgery (three of four patients), in follicular adenomas (five of nine patients), in Hashimoto's thyroiditis (two out of six patients, both belonging to a group of three with an early stage of the disease), and in paraadenomatous tissues (in three of nine patients). Interleukin-la positive TFEC were found less frequently than interleukin-6, and only in tissues with interleukin-6 positive TFEC. Only few interleukin-6 and interleukin-1α positive interstitial cells were found, even in the lymphocyte infiltrates (in both the autoimmune, benign or malignant disorders). In conclusion, both interleukin-6 and interleukin-1α could be demonstrated in TFEC from patients with autoimmune diseases, benign neoplasms or papillary carcinoma, whereas follicular cancer tissues were without interleukin-6 and interleukin-1α In contrast with previous studies, interleukin-6 and interleukin-1α were demonstrated in TFEC from patients with both Graves' disease and Hashimoto's thyroiditis, and the presence of these cytokines was related to the stage of the autoimmune process.