Antithyroid drugs is the first choice treatment of Graves' disease in China and Europe. However,the relapse rate is very high (40-60%) after therapy withdrawal, and many patients need further treatment. In our previous study, a new treatment strategy for GD has been introduced. After methimazole (18 months) combined with intrathyroid injection of dexamethasone (DEX) (3 months) treatment, the relapse rate of hyperthyroidism was markedly reduced compared with methimazole treatment alone (7.4% versus 51%) during the 2-year follow-up period. The results have been published in the 'J Clin Endocrinol Metab, 2009,94:4984-4991'. However, the mechanism by which the DEX reduces the relapse rate of GD is not fully understood. In vitro study, we have proven that DEX could effectively improve the function of regulatory T (Treg) cells and set up a new balance of T helper 1(Th1)/Th2 in GD patients(this results have been in press in the Eur J Endocrinol). In order to elucidate mechanism of this treatment strategy in vivo, we plan to recruit 20-30 patients with GD and treat those patients by intrathyroid injection of DEX combined with methimazole, and the function of Treg cells and balance of Th1/Th2 will be evaluated.