[en] A large sample (500) of thyrotoxicosis patients given iodine-131 treatment over the period 1968-1972 at the Radioisotope Laboratory of the Sofia Medical Faculty Chair of Roentgenology and Radiology have been studied. These patients underwent testing for radioiodine capture by the thyroid and scintigraphy, and hypothyrotic patients were subjected to the Hamolsky test and the TSH stimulation test. Estimations were made of the proportions of euthyrotic and hypothyrotic patients. In the group receiving TSH stimulation, various patterns of hypophysis/thyroid interrelations were revealed. One of the groups showed no response to thyroid stimulation; it consisted of cases undergoint complete, or nearly complete, radioiodine ablation of the gland. Another group of patients with radioiodine retention of myxedema type and clinical signs of hypothyrosis showed a normal thyroid stimulation response: these are likely to be cases of a secundary hypophysis-related hypothyroid reaction. Conclusions were drawn as to optimal single and total iodine-131 doses to be given is therapy of thyrotoxicosis. (author)