Human tongue preparations contain lipolytic activity similar to that present in human esophageal and gastric aspirates and in serous glands of rat tongue. The activity is present in homogenates of the glandular region (Ebner) beneath the cirumvallate papillae, and in secretions collected from the trough of the papillae. The lipolytic enzyme hydrolyzes long chain triglycerides to partial glycerides (di- and monoglyceride), glycerol, and free fatty acids at pH optimum 5.4. Lipolytic activity, expressed as nanomoles of triglyceride hydrolyzed per minute was in the range of 0 to 500 per gm. of tongue homogenate and 78 to 277 per ml. of aspirate from the vallate papillae. There was a 50% inhibition of the lipolytic activity by 4 mM sodium taurodeoxycholate. Specimens obtained from the region of the vallate papillae were examined by light and electron microscopy. Electron-dense granules similar to secretory granules present in rat Ebner's gland and in serous acini of human submaxillary glands were detected. Our findings suggest that in man, as previously reported in the rat, the lingual serous glands secrete a lipase that acts in the stomach where it initiates the digestion of dietary fat.