One of the commonly performed studies of thyroid function is the measurement of radioiodine uptake prior to radioiodine 131I therapy. Treatment using radioisotopes found recognition among many clinicians from all over the world. Therapy with 131I is successfully used in the reduction of non-toxic nodular goitres, in the treatment of hyperthyroidism in the course of Graves-Basedow disease, and in the treatment of toxic nodular goitres. Before the elective treatment, thyreostatics and other iodine-containing substances should be withdrawn, as they could affect the results of the radioiodine uptake test by inhibiting iodide accumulation in the parenchyma of an active thyroid.