SummaryThree new symptoms may appear when decrease of metabolism occurs in hyperthyroid patients treated by sulfo-compounds:1°a bruit and thrill over the thyroid;2°occasional increase of exophtalmos;3°light myxœdematous infiltration of the face.These symptoms are apparently the result of a«supranormal»liberation of thyrotropic hormone. Simultaneous treatment withœstrogens appears to inhibit the thyroid stimulation by an anti-thyroidectomy cell effect.The foundamental cause of the persistent thyrotoxicosis seems to reside in a functional disturbance of the pituitary gland.Functional thyroidectomy is obtained chemically by treatment with sulfo-compounds. Blockage of thyroid secretion leads to secondary readaptation of pituitary command mechanism in order to induce an increased thyroid activity.