he concentration of erythropoietin (EPO) in serum was studied. The study included 122 people divided into two groups. The main group (group 1) consisted of 102 patients with chronic obstructive pulmonary disease (COPD). The control group (group 2), comparable in age and sex, was 20 surveyed, with no signs of respiratory failure. The concentration of EPO was determined by the method of solid-phase enzyme immunoassay (ELISA) using the test system "Erythropoietin-EIA-BEST" (ZAO Vector-Best, Russia). The concentration of EPO in the serum of the patients of the main group significantly exceeded its content in the control group, the median and interquartile range were respectively 12.0 (7.4 - 16.1) mIU / ml in the main group and 7.5 (5.65-8 , 1) mIU / ml in the control group (p = 0.000454). The degree of increase in EPO correlated with the severity of COPD on the GOLD scale. In a pair comparison of the results obtained, significant differences were established between the control group and the G grade subgroup (p (control and C) = 0.021578), and the control group and subgroup D according to the GOLD classification (p (control and D) = 0,000721). An increase in the content of EPO in the blood is probably due to the reaction of the juxtaglomerular nephron apparatus to the formation of hypoxia due to a violation of the function of external respiration. Thus, the study of the concentration of EPO can be used to assess the severity of COPD, and in interpreting the results of this laboratory test, the possibility of increasing its concentration due to impairment of the function of external respiration should be considered.