Summary Extracts of various alimentary and related tissues from cattle of different ages were prepared and assayed for their esterolytic activity. Extracts of tissues from the tongue in the region of the vallate papillae, from the glosso-epiglottic area, from the pharyngeal end of the esophagus, and from the submaxillary salivary gland were higher in activity than extracts of tissues from the tongue in the region of the fungiform papillae, from the sublingual salivary gland, from the parotid salivary gland, from the portion of the esophagus distal to the pharyngeal end, and from the fundic and the pyloric regions of the abomasum. Extracts of the tissues from the tongue in the region of the vallate papillae, from the glosso-epiglottic area, and from the pharyngeal end of the esophagus of day-old calves were more active than extracts of corresponding tissues from older calves and mature cattle. The activity of extracts of the submaxillary and the sublingual salivary glands increased slightly with increasing age of animal.