In the first half of 2020, there were reports in the medical press about the presence of signs of polyorganic infection with coronavirus SARS-CoV-2. It was suggested that an additional role in the pathogenesis of COVID-19 hemoglobinopathy, hypoxia and iron overloading of cells of the parenchymatous organs. Based on these concepts and hypotheses, a system of pathogenetic therapy has been formed, but the positions of some hypotheses have not yet been confirmed by clinical studies. To clarify them, additional laboratory tests are required. Objective. To study peripheral blood parameters and their dynamics in COVID-19 patients treated with the diagnosis of «viral pneumonia» in the municipal hospital in Moscow from April to June 2020. Material and methods. Were examined 206 patients (82 men and 124 women) aged 26 to 97 years (average age 56.8±6.1 years) who were undergoing treatment in the 3rd department of GKB No. 15. O.M. Filatov with diagnoses: COVID-19 and pneumonia. 197 of them were discharged from the hospital, 9 died. The study of peripheral blood and counting of leukocyte formula were performed on Cobas Micro and Advia-21-20 analyzers (Simens, Germany). Biochemical studies were performed on spectrophotometer Getpremier (USA). Results. Analysis of the nature of changes in the number of leukocytes in the peripheral blood of patients with COVID-19 and pneumonia showed that cases of leukocytopenia were rare in patients (7% of patients), leukocytosis was detected in more than 20% of patients. The difference between the incidence of leukopenia and leukocytosis was 13.5%, but was not significant (p>0.2). Signs of lymphopenia were observed somewhat more frequently than lymphocytosis (in the evaluation of relative lymphocytosis - by 13.1%), but the difference was not statistically reliable. In assessing the number of lymphocytes in blood in patients with COVID- 19. Conclusion. The data obtained indicate a combined, multi-component pathogenic effect of COVID-19 virus on all three sprouts of hemopoiesis system in pneumonia patients: oppression of erythrocyte saturation processes with hemoglobin, erythropoiesis stimulation in some of them, change in platelet volume, formation of abnormal macroform plates, absence of reactive leukocytosis for acute inflammation, decrease in number of monocytic phagocytes and lymphoid cells. It is possible that some of these changes may affect the prognosis and the severity of the disease course.