alpha-Amylase in human serum consists of at least two isozymes originating from either the pancreas or salivary glands. These isozymes can be determined by three methods, electrophoresis, inhibitor method and antibody method. The committee on enzymes of the International Federation of Clinical Chemistry recommended the approved method for the catalytic concentration of alpha-amylase using 4,6-ethylidene-4-nitrophenyl-alpha-1,4-D-maltoheptaoside as a substrate. However, the assay method using 2-chloro-4-nitrophenyl-alpha-1,4-D-maltotorioside as a substrate is the IFCC method. On the other hand, the committee on enzymes of the Japan Society of Clinical Chemistry recommends an other method using maltoheptaose as a substrate. Various other methods are used as the routine method in clinical laboratories.