Petersen, P. Abnormal mitochondria in hepatocytes in human fatty liver. Acta path. microbiol. scand. Sect. A, 85: 413-4210, 1977. Liver biopsies from fatty livers in thirty patients whose daily alcohoh consumption was excessive, or they were in a diabetic state or overweight, and liver biopsies from seven control patients not presenting the above disorders, were studied by light microscopy 0.75 pm EPON embedded, tduidine blue stained sections, and electron miwoscopy. Abnormal mitochondria were rarely found in n o d liver tissue and, if present, they were found only in periportal hepatocytes. The frequency of hepatocytes containing abnormal mitochondria was significantly higher in fatty liver than in normal liver ( p < 0.01). These cePs were usually localized periportally, practically never in the centre od the lobule (p < 0.01). The occurrence of abnormal mitochondria was not correlated with the degree of steahosis, and the increase in number of abnormal mitochondria was equally high in alcoholists, diabetics, and overweight subjects. The dtrastructural appearance and the periportal localization suggest a hyperfunction of the mitochandria, which may prevent a development o f steatosis in these areas.