1. An elastase-like enzyme in plasma of patients with acute pancreatitis was purified by DEAE-cellulose column chromatography and polyacrylamide-gel disc electrophoresis.
2. In this way 0.24 mg of purified enzyme with a specific activity of 3.94 succinyl-l-alanyl-l-alanyl-l-alanyl-p-nitroanilide units/mg of protein was obtained from 10 ml of plasma.
3. The purified material was homogeneous as ascertained by sodium dodecyl sulphate/polyacrylamide-gel disc electrophoresis and had an apparent molecular weight of 24 000 as measured by gel filtration on Sephadex G-100.
4. This enzyme hydrolysed denatured casein and Congo Red—elastin as well as succinyl-l-alanyl-l-alanyl-l-alanyl-p-nitroanilide. Its amidolytic activity was inhibited by soya bean trypsin inhibitor, but not by aprotinin.
6. We propose that an elastase-like enzyme, probably different from elastase 1 or elastase 2, is liberated from the pancreas into blood during acute pancreatitis and becomes combined with α2-macroglobulin.