17-hydroxyprogesterone is a steroid hormone, it is synthesized from cholesterol in the adrenal glands, sex glands, placenta under the control of the ACTH level: it has pronounced daily fluctuations with a peak in the morning and the lowest level at night (it is recommended to evaluate the PDDC at 8.00 am), depends on the day menstrual cycle (MC) (it is recommended to evaluate for 3-5 days MC). It is synthesized in small amounts by the ovaries during the follicular phase, then its concentration increases in the luteal phase and remains constant during this phase. If fertilization does not occur, the level of the hormone decreases and, conversely, when the fertilized egg is implanted, the yellow body continues to secrete 17-hydroxyprogesterone. During pregnancy, the level is raised. It circulates in the blood in both free and bound states (mainly with albumin and transcortin). It is a precursor of cortisol and androstenedione (which is converted to testosterone and estradiol). The level of 17-hydroxyprogesterone is one of the markers (together with the levels of cortisol and androstenedione) in the diagnosis of PDCN caused by the deficiency of 21-hydroxylase (the main form of adrenogenital syndrome) or 17-hydroxylase . The decrease in the activity of 21-hydroxylase leads to a restriction of the possibility of conversion of 17-hydroxyprogesteronein cortisol, instead it accumulates and is sent to the cycle of biosynthesis of androgens. As a result, large amounts of androgens can cause severe progressive virilization, beginning with the fetal period and infancy. In addition, inadequate production of cortisol leads to the development of glucocorticoid insufficiency, the clinical manifestations of which will depend on the level of enzyme deficiency and require replacement glucocorticoid therapy. Because of the relatively high incidence of this disease and its severity, a new screening program for 17-hydroxyprogesterone has been introduced in some countries? . Monitoring of the concentration of 17-hydroxyprogesterone is necessary for replacement steroid therapy. In addition, the study17-hydroxyprogesterone in response to parenteral administration of synthetic ACTH is performed to confirm the alleged diagnosis of a "partial" deficiency of 21-hydroxylase , as a possible cause of female hirsutism and infertility.