The Zn concentration in thyroid tissue and whole blood of patients with Graves' disease, thyroid cancer, and nodular goiter disease was determined using the total-reflection X-ray fluorescence method. The dependence of obtained concentrations on the clinical stage of the examined disease, histopathological grading, and kind of analyzed material (thyroid tissue and blood) was studied. The determined concentration of Zn was the lowest in the thyroid tissue of patients with thyroid cancer (23.1 microg/g) and it was the highest in the case of Graves' disease (41.7 microg/g), whereas in the blood samples, the reverse results were found (7.1 microg/g and 4.8 microg/g, respectively). The physical basis of the method used, the experimental setup, and the procedure of sample preparation are described.