Abstract
The sensitive immunoperoxidase method was used to localize kallikrein in the submandibular gland of the cat, guinea pig, dog, and man. In every instance, kallikrein was localized in the apical region of duct cells, a location suggesting its secretion into the duct system. There was no evidence of the enzyme in other cells or interstitial tissue in the gland. The major source of submandibular gland kallikrein, therefore, must be of ductal origin. The classification of kallikreins with the widely distributed group of serine proteases is discussed, as is their possible significance in regulating physiological processes by specific and limited proteolysis.