Abstract: The T₃ suppression test,jndged by the serum T₄ and the 4-h thyroidal ¹³¹I uptake,was carried out in 67 patients with Graves’ disease 2 weeks to 3 months following cessation of an tithyroid drug therapy and repeated in 40 of these patients 12—18 months later.A good correlation was shown between the decrease of the serum T₄ and the per cent fall of the thyroidal ¹³¹I uptake before and after T₃ administration（r=0.659,P＜0.01）.Consistency of the suppressibility or the unsuppressibility by the two indices was observed in 82.1% of the 67 patients at initial examination and in 87.5% of the 40 patients at re-examination.Relapse occurred in 6.9% of the patients with the suppressibility by serum T₄ and in3.2% of the patients with the suppressibility by thyroidal ¹³¹I uptake（P＞0.05）.It occurred in 34.2% of patients with unsu ppressibility by the serum T₄ and in 38.9% of the patients with unsuppressibility by the thyroidal ¹³¹I uptake（P＞ 0.05）.There was significant difference between the relapse retes in patients with suppressibility ane the patients with unsuppressibility by either of the serum T₄ and the thyroidal ¹³¹I uptake（P＜ 0.05）.The present study showed that the two indices of the test have a close relationship and both could be useful in predicting prognosis of Graves’ disease.