[en] A solid-state RIA method using a plastic microtiter plate for human TSH was developed: The choice of carrier protein for standard TSH was critical in this method and pooled sera from untreated Graves patients was found to be suitable for this purpose. The mean lowest detectable TSH level was 0.2 μU/assay, which was almost equal to those reported by other methods. This method is superior because of the simplicity of its assay procedure, especially in the separation of bound and free TSH and in the shorter incubation time required in the double antibody method. Serum TSH concentration in 22 normal subjects, 17 patients with Graves' disease, 35 with Hashimoto's thyroiditis, 18 with primary hypothyrodism, 16 with simple goiter, 4 with nodular goiter and 7 with secondary hypothyroidism was estimated as 4.7+-2.0 μU/ml (mean +- s.d.), 2.1+-0.2 μU/ml, 14.1+-26.5 μU/ml, 211+-177 μU/ml, 3.6+-2.4 μU/ml, 3.2+-2.4 μU/ml and 2.6+-1.0 μU/ml, respectively. A statistically significant and hyperbolic inverse correlation (r=-0.37, N=90) was found between TSH and T4 levels. (JPN)