WE have reported in earlier communications1,2 that the extract of fresh pancreas as well as that of acetone-dried pancreas powder contains a specific enzyme which we called 'elastase'. This enzyme had not been found before in the human or animal organism ; but it was studied first by Eijkman3 so early as 1904 as a product of bacteria. The elastase of the pancreas dissolves the elastic fibres of the arteries. We found that in the wall of the arteries only the elastic fibres are attacked by this ferment, and the collagen remains unaltered. We have been able to show that our pure elastase differs from other proteolytic ferments of the pancreas such as trypsin and chymotrypsin. Through the kindness of Dr. J. H. Northrop, of Princeton, N.J., we obtained crystalline trypsin and chymotrypsin, and we tested the elastolytic power of these enzymes parallel with our elastase. Neither trypsin nor chymostrypsin exercises any dissolving effect upon the elastic fibres of the arteries ; therefore, we can conclude that the elastase is not identical with the known proteolytic enzymes.