Aldolase (EC 4.1.2.13) plays an important role in glucose metabolism. Aldolase has a molecular weight of 160 kDa and has three isozymes, namely aldolase A, B and C. The enzyme is probably present in all cells; it occurs in particularly large quantities in the muscles, liver and brain. An increase in serum aldolase is found in myotonic muscular disease, such as progressive muscular dystrophy and polymyositis. The enzyme rises in myocardial infarction, reaches a maximum within 24-48 hours and returns to normal in the course of five days. In these muscular diseases, aldolase A isozyme is elevated. Aldolase activity, especially B isozyme, in serum rises to very high levels in acute hepatitis, but is slightly elevated in cirrhosis, chronic hepatitis and obstructive jaundice. Aldolase becomes elevated in serum with malignant tumors, and isozyme A is predominant in serum. Erythrocytes are also rich in aldolase, and the enzyme rises in hemolytic anemia.