Alanine aminotransferase in clinical practice. A review. Alanine aminotransferase is an enzyme produced mainly in the liver. When serum activity is measured, it provides a marker of hepatic disease. This review explores the biochemistry and laboratory analysis of alanine aminotransferase in terms of its significance in human health and disease. Cut-off levels that define abnormality are rather arbitrary and this decreases the specificity of the test in apparently healthy patients. A small, but important, group of patients with alanine aminotransferase abnormality have underlying liver disease that may be treatable. Most can be diagnosed based on history, physical examination, and biochemical-serological profiles. Liver biopsy can complement the diagnostic process in selected circumstances. Literature pertaining to this is critically reviewed. 