The purpose of this study was to ascertain 1) fatty infiltration of the liver in spontaneously ketotic cows and 2) the most appropriate blood components to aid diagnosis of ketotic fatty liver. Liver biopsies and blood samples were obtained under field conditions. Cows were divided into three groups (healthy, mildly ketotic, and severely ketotic) by their blood ketone body concentrations. Severely ketotic cows had a greater percent fat in the liver than healthy cows. The mildly ketotic group fell between the other two groups and was significantly different from only the severely ketotic group. There was a positive correlation between fatty infiltration and blood ketone body concentrations but a negative correlation with glucose concentrations. Liver-specific enzymes were positively correlated with fatty infiltration. Only ornithine carbamoyltransferase and iditol (sorbitol) dehydrogenase could be used to separate healthy cows from those with severe ketosis. The best equation to explain the variation of percent fat in liver included concentration of beta-hydroxybutyrate (BHB) and logarithm of ornithine carbamoyltransferase concentration (Log-OCT): % Fat = -6.15 + 2.39 (BHB) + 11.7 (LogOCT) Although this equation explained 39.5% of the variation, it could not be used to predict reliably percent fat in the liver. Liver biopsy seems still to be the only reliable method of measuring of fatty infiltration in the liver.