TTF1 mRNA expression in the thyroid gland from 30 patients with thyroid proliferating diseases and 4 healthy donors used as normal controls was investigated using Northern blot analysis. Six patients affected by malignant thyroid carcinomas and six patients with adenoma were examined; moreover 18 patients with non malignant proliferating disease such as multinodular goiters were investigated. Determination of TTF1 mRNA revealed a significant decrease of the steady state mRNA levels in carcinomas and adenomas as compared to normal tissues. On the contrary, in patients affected by multinodular goiters variations were observed that seemed not to be directly associated with the pathological conditions.