FIELD : medicine.SUBSTANCE : invention relates to the field of medicine, namely hepatology, and can be used to determine the degree of liver fibrosis. Patient is subjected to 13C-methacetin breath test. Using cumulative dose values 13C for the time of 10, 20 and 30 minutes of this test, determine the degree of liver fibrosis by the formula : N=1a+2b+10c, where – N is the sum of the points, a is the coefficient calculated from the cumulative dose 13C in 10 minutes in % (CUM10), b is the coefficient calculated from the cumulative dose 13C in 20 minutes in % (CUM20), c is the coefficient calculated from the cumulative dose 13C in 30 minutes in % (CUM30). If CUM101.00?%, a=0. If CUM202.50?%, b=0. If CUM305.65?%, c=0. If N=0, determine the degree of liver fibrosis as F0, corresponding to the absence of portal fibrosis. If N=1–3, the degree of liver fibrosis is determined as F1-2, corresponding to the presence of portal fibrosis without septa and with a small amount of septa. If N=10–13, the degree of F3-4 liver fibrosis is determined, corresponding to the presence of numerous septa without cirrhosis and cirrhosis.EFFECT : method provides the possibility of non-invasive determination of liver fibrosis through the use of 13C-methacetin breath test.1 cl, 4 dwg, 9 tbl, 2 ex