Elastases are unique among the proteases in that they are capable of hydrolyzing the scleroprotein elastin. The enzymes include pancreatic elastases 1 (Protease E) and 2, and neutrophil elastase. These three elastases also have esterase and amidase activity toward synthetic substrates such as succinyl-trialanine-p-nitroanilide. Although the three enzymes are similar to each other in enzyme activity, they are quite different in immunoactivity. Therefore, each elastase has its own specific immunoassay either by RIA or EIA. Serum immunoreactive pancreatic elastases reflect disease conditions of pancreatic diseases, especially acute pancreatitis and pancreatic cancer. On the other hand, serum neutrophil elastase increases in various inflammatory diseases or conditions.