The radioimmunoassay of TSH (human thyrotropin) was performed by utilizing anti-h-TSH antibody and purified human thyrotropin supplied from Daiichi from Jan. 1978 through Aug. 1980 the serum concentration of TSH was measured on 41 cases with various thyroid diseases, and 22 normal persons. Among 41 cases, 9(22%) were primary hypothyroitlism, 17(41%) Graves' disease, 8(20%) subacute or chronic lymphocytic thyroiditis, and 7(17%) nodular goiter. The results were as follows:1) The normal values of serum TSH in 22 cases of control group were 4.2±1.7μU/ml, (1.9∼7.4μU/ml), which were within normal range in kit used in this study. 2) The serum TSH concentration in 9 cases with primary hypoehroidism were 97.1±116.4μU/ml(14. 0∼300μU/ml), which were significantly elevated as compared, with normal control values. 3) The serum TSH concentration in 17 cases with Graves' disease were 1.5±0.6μU/ml(1.0∼2.5μU/ml), which were below than normal control. 4) The serum TSH concentration in 8 cases with subacute or chronic lymphocytic thyroiditis revealed wide ranges(1.6∼220μU/ml), according to the state of thyroid function. 5) The serum TSH values in 7 cases with nodular goiters were 2.3±2.0μU/ml, which were strictly within normal levels. 6) The serum TSH levels were elevated during prolonged treatment with Tapazole(Methimazole) without serial check of the serum TSH concentration in Graves' disease, so the serial measurement of serum TSH concentration was considered of available index of thyroid states.