Measurement of the alanine aminotransferrase-(ALT) and aspartate aminotransferase (AST) activity in the serum has been used to identify patients with liver disease for more than 50 years. While isolated moderate to strong elevations of ALT and AST typically indicate specific liver disease, mild elevations of aminotransferases can be observed in widespread diseases, e.g., metabolic syndrome. Various studies were able to show an association between elevated liver enzymes and liver associated mortality as well as overall mortality. Aminotransferase values in the general population vary with gender, age and ethnicity and studies show that current broadly applied upper limits of normal for ALT and AST are unreliable for sensitively detecting or excluding significant liver disease. However, the measurement of these liver enzymes remains an important tool in the official diagnostic & treatment decision process.