Abstract: Summary. 13C-metacetin breath test is a non-invasive, non-radioactive, sensitive and specific method for determining the functional activity of hepatocytes, liver cell failure and stages of fibrosis. Objective: study the possibility of assessing the functional state of the liver with cirrhosis of various etiologies with the help of index DOB20. Materials and methods. The study included 90 patients (30 patients with liver cirrhosis of alcoholic etiology and 30 patients with liver cirrhosis of viral etiology and 30 healthy volunteers (control group). All patients with cirrhosis were divided into three equal groups of 10 people, depending on their indicators on the Child-Pugh scale. All patients underwent standard clinical, laboratory and instrumental examination and 13C-metacetin breath test: both the standard method and the modified method. Results. The revealed direct strong correlation between the indices of the 13C-metacetin test at 20 minutes and 120 minutes allows the use of the DOB20 indicator to determine the mass of functioning hepatocytes. Using the DOB20 indicator instead of the “cumulative dose” indicator allows you to significantly speed up the study and reduces its cost. Indicators of the 13Cmetacetin test at 20 minutes allow us to evaluate the functional state of hepatocytes and also closely correlate with the classes of liver cirrhosis on the Child-Pugh scale.