Transaminases or aminotransferases are a group of enzymes that catalyze the transfer of an amino group from an alpha amino acid to an alpha-keto acid reversibly. It is known as transamination. All naturally occurring a-amino acids participate in transamination except lysine, threonine and proline. Transamination is an important mechanism in metabolism of amino acid. Two clinically important transaminases enzymes are aspartate aminotransferase (AST) or serum glutamate-oxaloacetate transaminase (SGOT) and alanine aminotransferase (ALT) or serum glutamate-pyruvate transaminase (SGPT). This chapter covers the transamination reaction, estimation of serum ALT OR SGPT, normal range, and estimation of serum AST or SGOT.