A convenient lipase assay that discriminates between pancreatic and lingual lipase activities was developed to describe some properties of the triglyceride-hydrolyzing activities of lingual lipase (from von Ebners glands) and pancreatic lipase. Secretion of lingual lipase is stimulated by feeding. Gastric contents collected postyprandially from patients with cystic fibrosis (CF) contained lipase activity which is probably secreted from pharyngeal tissues. Also, duodenal contents from CF patients contained lipase activity with properties very close to those found in gastric contents from CF patients and controls. Apparently, the serous glands responsible for the secretion of lingual lipase is less affected than the exocrine pancrease in this disease. During fat balance experiments, CF patients utilized around 40% of the dietary lipids and more than 50% of milk lipids given as a test meal were hydrolyzed in the duodenum within 2 hr. In these patients with severe pancreatic insufficiency, we suggest that the lingual lipase is responsible for a considerable proportion of triglyceride hydrolysis. This hydrolysis starts in the stomach and continues in duodenum.