To study the adaptive response of lingual lipase and pancreatic lipase to dietary fat, three sets of experiments were performed in adult male rats. In the first experiment, rats were fed for 3 wk a low fat diet (4.5% fat) or a 10, 20 or 30% fat diet. In the second, rats were fed a 4.5% fat diet for 4 wk or a 20% fat diet for 1, 2 or 4 wk. In the third, rats were fed for 3 wk a 10% fat diet with various sources of fat (lard, sunflower oil, olive oil, peanut oil, butter, soybean oil, corn oil or salmon oil). The results demonstrated that 10% dietary fat was sufficient to promote a maximum significant increase in lingual lipase activity (expressed in units/g tissue and in units/mg protein), whereas pancreatic lipase responded steadily to 20 and 30% fat diets. After 1 wk of feeding 20% dietary fat, both enzyme specific activities had reached their maximum values. The fatty acid composition of dietary triglyceride molecules (chain length, number and location of double bonds) had no specific effect on the adaptation of lingual lipase. The physiological implications of these findings are discussed in regard to the role of intragastric lipolysis in fat digestion.