We measured the populations of mutated mitochondrial DNAs with the 7,436 bp or the 4,977 bp deletion from apparently normal human liver and human livers with chronic hepatitis, cirrhosis, and hepatocellular carcinoma. The amount of the mutated mitochondrial DNA was at the same level between normal and chronically hepatitic livers but was significantly lower in human livers with cirrhosis and hepatocellular carcinoma, especially the latter, suggesting that the mutated mitochondrial DNAs may be decreased with the progress of liver disease from chronic hepatitis to cirrhosis and hepatocellular carcinoma. This phenomenon is opposite to that occuring in the ageing process.