Highly sensitive methods for determining the level of TSH, carried out using test kits of the second and third generation, make it possible to differentiate with high accuracy the normal and subnormal levels of TSH in the blood and are currently widely used to examine patients with thyroid pathology. These methods have been used for a long time in clinical practice in the United States of America, and recently they are also increasingly used in Russia. The level of TSH below normal values is determined in almost all cases of hyperthyroidism (with the exception of cases of TSH-secreting pituitary adenoma or resistance of the pituitary to thyroid hormones), which makes it possible to do without additional testing with tyroliberin (TRH). Methods for determining second generation TSH usually have a lower sensitivity limit of about 0.1 mU/L. When using the third generation methods, it is possible to accurately determine the level of TSH up to 0.01 mU/L. The fourth generation methods, which are still under development, will have a lower limit of determination of 0.001 mU/L, but they are unlikely to be used for routine clinical studies in the near future. At the Endocrinology Research Center of the Russian Academy of Medical Sciences in Moscow, third-generation methods are currently being used for routine clinical research (the Amerlight system, produced in Russia by the Amerkard joint venture). In addition to this system, other test systems of both domestic and foreign production are also available in Russia. In the USA, methods for determining TTG of the second and third generation are used. Third-generation systems are noticeably more expensive than second-generation systems. Given that in most patients with hyperthyroidism, the TSH level is in the range of less than 0.1 mU/L, methods for determining the third generation are more preferable. In general, the normal level of TSH in the blood of individuals in a state of euthyroidism is from 0.5 to 5.0 mU/L, although there are some interlaboratory differences in the standards for the level of TSH.