Fifty-three histologically proved cases of various diffuse liver disease were studied for their computed tomography numbers (CTN). The machine used was Ohio Nuclear's Delta Scanner 50FS type and CTN was expressed by the Hounsfield unit (H). Mean CTN in each group was as follows: 66.6 +/- 2.6 H in normal control (N), 63.3 +/- 6.0 H in chronic hepatitis (CH). 61.8 +/- 7.0 H in liver cirrhosis (LC), and 44.4 +/- 10.6 H in fatty infiltration (FI). There were no significant differences among them except FI group. As N group were all above 60 H and CH and LC groups were all above 50 H, CTN below 60 H suggests chronic liver disease or fatty infiltration and CTN below 50 H strongly suggests fatty infiltration. In eleven cases where total lipid content of the liver could be be biochemically determined by the sulfo-phospho-vanillin reagent, a relation of total lipid content to CTN was studied. As a result, a significant correlation existed between them (r = -0.89; p less than 0.001). If the diagnostic criterion of fatty liver was set at total lipid content above 100 mg/g wet liver, CT criterion was estimated at CTN below 48 H from the regression formula.