Abstract: The serum thyrotropin (TSH) concentrations of 1631 patients were measured with immunoradiometric assay (IRMA) by two kind of kits. The results obtained show that the sensitivity of TSH IRMA in the diagnosis of thyrotoxicosis and hypothyroidism is excellent; but the specificity is not good enough. It can not yet replace other thyroid function tests, but it is clearly emerging as an important means of screening patients for thyroid dysfunction. Interpretation of the TSH value should be made with a clear understanding of its limitations.