Elastase is a serine protease that catalyzes not only the hydrolysis of peptide bonds of proteins but also the hydrolysis of amides and esters. Although it has similar functions as trypsin and chymotrypsin, elastase preferentially targets the protein elastin catalyzing cleavage at its neutral sites. Two major types of elastase have been identified, including pancreatic elastase and neutrophil elastase (PMN). While he pancreatic elastase is produced initially as an inactive protein requiring the activation by trypsin in the duodenum; PMN is found in relatively high levels in the azurophilic granules of circulating leukocytes and neutrophils. Both types of elastase exhibit similar activities but differ in substrate specificity and inhibitor profile.