Knowledge concerning the structure and quality of thyroglobulin (Tg) has great significance for the better understanding of the pathogenesis of different thyroid diseases. The localization of the Tg gene and studies of its structure by molecular biological techniques make possible precise investigations of its expression. The aim of our study was to evaluate Tg content in the thyroids and Tg concentrations in the serum of 108 patients suffering from benign or malignant thyroid disorders. The method of investigation was isolating total protein from thyroid tissues obtained during surgery and determining Tg content in the thyroid extracts and Tg concentrations in serum. The Tg concentrations in serum and in thyroid protein extracts were evaluated by fluoroimmunometric assay. Statistical analysis was carried out with the help of the computing programmes.