Blood tests such as aminotransferases are indicators of liver cell injury not liver function, so it would be more appropriate to call them liver tests instead of liver function tests. Liver tests should be interpreted in a clinical context, and follow-up tests are often helpful to assess liver diseases. Abnormal liver tests in apparently healthy individuals can be categorized into four types: ① isolated elevation of serum bilirubin; ② isolated elevation of serum alkaline phosphatase (ALP); ③ hepatocellular injury; and ④ intrahepatic cholestasis. Mild unconjugated hyperbilirubinemia without any other test results is frequently suggestive of Gilbert syndrome, which needs no specific therapy, but the possibility of hemolysis should be ruled out. An isolated elevation of ALP can be due to non-hepatic causes such as normal rapid growth, pregnancy, or bone diseases. The source of the elevated ALP can be considered to be of hepatic origin if gamma-glutamyl transpeptidase (GGT) increases simultaneously. GGT also increases after chronic ethanol ingestion. A significant elevation of ALP also occurs in infiltrative lesions of lymphoma or leukemia. Up to 25% of asymptomatic testees show a mild elevation of aminotransferases. A substantial proportion of them have parenchymal liver diseases such as fatty liver, chronic hepatitis, or early cirrhosis. A history of exposure to hepatotoxins, physical examination, and tests for viral markers are helpful. If ALT is normal, the increased AST is highly likely to be of muscle origin. Serum ALP and GGT increase mainly in intrahepatic cholestasis, and early stage of primary biliary cirrhosis or drug-induced cholestasis should be considered.