Pancreatic extract contained an enzyme which dissolved the elastic fibers of the aorta wall and which was called elastolytic enzyme or elastase. Trypsin prepared according to Kunitz and Northrop had little effect on arteries. The elastase dissolved only the elastin in the aorta wall and left the collagen unchanged. Elastase did not liberate amino acids from the aorta wall, but insoluble elastin was changed into a soluble protein. The pH optimum of the elastase (10.3) was more alkaline than that of trypsin.