SUMMARY Liver biopsy was performed in 38 patients with fulminant hepatitis and coma and repeated in 22. Stereological estimation of hepatocyte volume was correlated with levels of clotting factors.Early liver biopsy allowed prognosis in 55 % of the cases. All patients with a hepatocyte volume of <35% and thromboplastin time <10% died; all patients but two with hepatocyte volume > 350%and thromboplastin time > 10% recovered consciousness (n = 9) or at least showed evidence of marked liver regeneration (n = 2).On serial liver biopsy a significant increase in hepatocyte volume and clotting factors was only observed in patients who recovered consciousness. The estimated liver cell mass after regeneration in patients who recovered consciousness was > 45 and <45 % in the patients who did not.The very sophisticated treatments recently introduced for the treatment of acute hepatic failure point to the need for quantitative parameters of liver function and liver regeneration in order to decide which is the most adequate treatment and the best moment to start it.The aim of this study is to estimate the severity of liver damage by early liver biopsy in patients with acute liver failure; the ability of the liver to regenerate demonstrated by serial liver biopsies; and a correlation of this parameter with liver function reflected in coagulation studies. PatientsDuring the past seven years. 106 patients were admitted in coma and acute liver failure due to viral hepatitis (104 cases), mushroom poisoning (one case), and INH overdose (one case). In 10 patients coma did not exceed grade III and all survived. Of 96 patients in coma grade IV, 24 (25 %) recovered consciousness and 18 (18.7 %) survived.Early liver biopsy (one day before to five days after the onset of coma) was performed in 38 patients (fig 1), using a Menghini 1-4 mm needle. Clotting fractions (PPSB or antihaemophilic concentrated plasma)