Liver lactate dehydrogenase (LDH) isoenzymes in normal and diseased cows were analyzed electrophoretically. This method (histoelectrophoresis) was improved for the direct analysis of tissue LDH isoenzymes. The mean values of LDH1 through LDH5 in the livers of normal cows were 31.7, 24.8, 27.3, 12.8, and 3.3%, respectively. In cases with hydropic degeneration of the liver, the patterns revealed increases of LDH1 and LDH2 as compared to normal cows. The patterns showed a decrease of LDH1 and an increase of LDH2 in fatty change of the liver. Congestion of the liver alone decreased LDH1 and increased LDH3, LDH4 and LDH5. Necrosis of the liver decreased LDH1 and LDH2, and increased LDH3, LDH4 and LDH5. It was suggested that the functional hepatocellular damage due to anoxia might be a important factor of the change of liver LDH isoenzyme patterns. We have attemped to standardize the LDH isoenzyme patterns by using a computer under various conditions. In cases with hydropic lesions, the diagnostic sensitivity (DS) was 53% (28 of 53 cases) and the predictive value of positive tests (PVPT) was 100% (28 cases of 28 cases selected). In cases with congestive or necrotic lesions, DS was 41% (9 of 22 cases) and PVPT was 69% (9 cases of 13 cases selected).