Thyroid-stimulating hormone (TSH) or thyrotropin is a glycoprotein secreted by the thyrotropic cells of the anterior pituitary gland. Its main function is the regulation of the synthesis and secretion of the thyroid hormones which are inevitable for normal evolution of newborn brains and their normal growth. An early detection of neonatal TSH level is necessary for quick diagnosis and efficient therapy. As the concentration of TSH in uncured newborns tends to increase irreversibly, the early direct and sensitive determination of TSH gives possibility to reveal the early stage of the disease, primary hypothyreosis. This assay is intended for the measurement of newborn TSH, eluted from dry blood spots.