Measurement of antimitochondrial antibodies is established as a sensitive indicator for primary biliary cirrhosis, which has unfortunately limited diagnostic specificity. M2-antigen complex, consisted of four proteins of the inner mitochondrial membrane, has been found to be strongly associated with PBC. Clinical value of anti-M2 antibodies quantitative measurement with ELISA was analysed in 107 patients with carefully diagnosed liver diseases: acute viral hepatitis A, B, C (VHA, VHB, VHC; n = 41), chronic viral hepatitis B, C (CHB, CHC; n = 23), autoimmune hepatitis (AH; n = 6), liver cirrhosis (LC; n = 20), extrahepatic cholestasis (EC; n = 2) and primary biliary cirrhosis (PBC; n = 15). The highest values were found in PBC patients and varied from 92 to 167 U/l and dramatically exceeded normal range recommended by manufacturer (5 U/l). Mean value in this group (119.5 +/- 8.4 U/l) was significantly (p < 5 x 10(-8)) higher than in others, that varied from 1.3 +/- 0.2 up to 2.8 +/- 1.7 U/l in VHA and CHC groups respectively. Only two among 92 non-PBC patients have values over 10 U/l, but they reached only 15.8 (CHB) and 16.5 (CHC). Anti-M2 level in PBC patients demonstrated a significant positive correlation (r = 0.857) with the degree of liver insufficiency measured trough Child-Pugh score. From these data we can conclude, that quantitative measurement of anti-M2 antibodies with ELISA can serve as a very good screening for PBC, with 100% diagnostic sensitivity and specificity, if concentration of 20 U/l will be established as a pathognomic level.