The ratio of the serum aspartate to alanine amino-transferase levels (AST/ALT) is often used as a clue to the etiology of the underlying liver disease. This ratio is usually greater than 2.0 in alcoholic liver disease and less than 1.0 in patients with chronic hepatitis and chronic cholestatic syndromes. We analyzed the AST/ALT ratio in 177 patients with various forms of nonalcoholic chronic liver disease who underwent medical evaluation and percutaneous liver biopsy. In the majority of cases of chronic viral hepatitis, the AST/ALT ratio was less than 1.0. However, there was a statistically significant correlation between the AST/ALT ratio and the presence of cirrhosis. Among 100 patients with chronic type B hepatitis, the mean AST/ALT ratio was 0.59 in those without cirrhosis and 1.02 in those with cirrhosis. Furthermore, the AST/ALT ratio often rose to greater than 1.0 when cirrhosis first became manifest. Thus, the finding of an AST/ALT ratio of greater than 1.0 in a patient with nonalcoholic liver disease should suggest the presence of cirrhosis. In addition, the use of the AST/ALT ratio as a means of separating alcoholic and nonalcoholic liver disease must be tempered with the knowledge that this ratio may be less helpful in the presence of cirrhosis.