Physicians frequently order batteries of tests that are used to assess liver injury or function. These tests are frequently ordered to screen for disease. However, a lack of understanding of the nature of the assays and the laboratory assignment of normal versus abnormal often leads to unnecessary workup or missed disease. We attempt to describe the nature of the most commonly used laboratory tests for liver disease, including alanine and aspartate aminotransferases, alkaline phosphatase, bilirubin, and gamma glutamyl transpeptidase. In addition, the role of functional tests of the liver, including prothrombin time, and metabolite clearance tests, such as aminopyrine and monoethylglycinexylidine, are examined.