Abstract: After intraperitoneal injection of tartar emetic at the dosage of 15 mg/kg or ammonium antimonyl gluconate at the dosage of 60 mg/kg to rats once a day for fourteen days, a dose of I¹³¹ of 0.24 microcurie was administered intraperitoneally. The animals were sacrificed 24 hours after the I¹³¹ administration and the radioactivity in the thyroid was measured. The I¹³¹ up-take by the thyroid of the tartar emetic treated or of the ammonium antimonyl gluconate treated rats was not significantly different from that of the control animals. It is concluded that continuous administration of these antimonyl compounds to rats for two weeks does not affect the thyroid function.