The probability of formation of the so-called “cytokine storm” accompanied by an avalanche-like growth of inflammatory markers - interleukins (IL)-1β, -6, interferon-γ, tumor necrosis factor-α, C-reactive protein (CRP), ferritin, etc. is high at a heavy current of COVID-19. In the absence of adequate treatment in the development of “cytokine storm” increases the risk of death, especially against the background of comorbid pathology. Methods. In April-May 2020, patients (n = 28: 12 men, 16 women; age 39 - 86 years) with long, chronic COVID-19 course were under observation, hospitalized on critical days of the disease. All patients reported anosmia, cough with poor sputum, signs of conjunctivitis. The patients had chronic diseases (n = 22: coronary heart disease, diabetes mellitus type 2, scleroderma). All patients were given standard therapy; half (n = 14) were additionally prescribed Laennec for 3 - 10 days (6 ml per 350 ml of 0.9% NaCl solution, intravenous infusion for the first 3 days, from day 4 - 6 ml per 250 ml of 0.9% NaCl solution) until stable remission is achieved. Results. The majority state (n = 25) stabilized; several patients died in the control group (n = 3; p = 0.067). In spite of the state stabilization, no reliable positive dynamics was noted in the control group for the tested parameters. Initially, liver dysfunction (level of alanine aminotransferase (ALT) - 113 ± 121, aspartate aminotransferase (AST) - 90.8 ± 87) was registered in 71% of patients, 8 units/l) and high risk of “cytokine storm” development (ferritin levels in men - 480 - 1 072 µg/l, in women - 274.7 - 493 µg/l, C-reactive protein - 5.0 - 52.6 mg/l, lymphocytes - < 25%). Positive clinical dynamics, a decrease in the level of ferritin (-282 µg/l - in men, -80 µg/l - in women; p = 0.039), an increase in blood oxygenation to normal values (p = 0.0029), a decrease in the area of lung injury according to CT data (on average - 10%); p = 0.0027), increase in relative lymphocyte content (+8%; p = 0.04), normalization of markers of liver dysfunction (AST, ALT), creatinine and systolic blood pressure (p < 0.05) were observed on prescription of Laennec. All patients who received Laennec recovered within 3 - 15 days from the start of the drug and were discharged with a negative test for SARS-CoV-2. Conclusion. Health condition is significantly improved, a wide range of hepatoprotective, immunomodulatory and regenerative effects are observed when the polypeptide Laennec is included in the complex therapy in patients with severe COVID-19. Laennec should be used primarily in patients with liver pathology, diabetes mellitus type 2, coronary heart disease, including high ferritin levels.