We report here the use of the biochemical marker desialylated transferrin to aid in the diagnosis of nonalcoholic steatohepatitis. Conventional biochemical tests used for the detection of chronic alcohol consumption fail to differentiate nonalcoholic steatohepatitis patients from alcoholic subjects. In addition, even in those alcoholic subjects with alcoholic liver disease in whom biopsy has been performed, it is impossible to differentiate these two disease states on the basis of morphological examination alone. In this study we have examined two new markers of excessive alcohol intake, desialylated transferrin and mitochondrial AST in subjects with nonalcoholic steatohepatitis and in patients consuming excessive amounts of alcohol. All nonalcoholic steatohepatitis patients consumed minimal or no alcohol and were diagnosed by morphological criteria based on liver biopsy specimens. Alcoholic subjects were consuming in excess of 80 -/day ethanol, often with clinical evidence of overt alcoholism. Control subjects included both healthy controls and patient controls with liver diseases unrelated to alcohol. The ratio of desialylated transferridtotal transferrin was elevated only in patients who consumed excessive amounts of alcohol, whereas the ratio of mitochondrial AST to total AST (mitochondrial AST/total AST) was not significantly different between alcoholic subjects and patients with nonalcoholic steatohepatitis. The sensitivity and specificity for the ratio desialylated transferridtotal transferrin was 81% and 98% respectively, whereas the sensitivity for the mitochondrial AST/total AST ratio was 92%; the specificity was only 50%, indicating that there were a large number of false-positives. All the conventional markers were less sensitive and less specific than the ratio desialylated transferridtotal transferrin. We conclude that it is possible to differentiate patients with nonalcoholic steatohepatitis from patients consuming excessive amounts of alcohol using the biochemical marker desialylated transferrin but not mitochondrial AST. Mitochondrial AST is useful only in