Lingual lipase (LL) activity, pH, and products of fat hydrolysis were determined in gastric aspirates from preterm infants who received formula milk feeds by a nasogastric tube. In 1-hourly (n = 9), 2-hourly (n = 8) and 3-hourly (n = 9) fed infants LL activity increased to reach its maximum value at 60, 90, and 120 min respectively after the feeds, and gastric pH levels fell from about 6.0 to less than 3.5. There was a reduction in triglyceride content to 50% of the initial value, measured immediately after a feed, and the products of hydrolysis were mainly diglycerides and FFA. In a subsequent study 3-hourly fed infants (n = 8) had a tube feed followed by a bottle feed, and then a bottle feed followed by a tube feed on successive days (cross-over). The LL activity observed after a bottle feed (mean maximal value 23.8 mumol FFA/ml/h) was significantly higher than after a tube feed (19.1 mumol FFA/ml/h). It is suggested that substantial triglyceride hydrolysis takes place in the stomach due to lingual lipase, and sucking seems to enhance enzyme production.