The origin of preduodenal lipases was investigated in the suckling dog. In this species, gastric lipase is the main (or only) preduodenal lipase (activity range 1.03-8.32 U/mg protein), lingual-lipase activity being absent or amounting to traces only (0.77-2.3 mU/mg tissue). The localization of lipase activity in the stomach was mapped and compared to that of pepsin. The data show that the highest lipase activity was found in biopsy specimens of gastric mucosa from the cardia area (5.32 +/- 1.29-8.32 +/- 0.93 U/mg protein), and the lowest in the antrum (1.03 +/- 0.16-1.94 +/- 0.43 U/mg protein). Activity was also significantly higher in the mucosa along the greater rather than the lesser curvature of the stomach. Pepsin activity was highest in the cardia and gastric body areas (26.2 +/- 0.89-89 +/- 23.61 and 26.83 +/- 15.98-69.51 +/- 9.82, respectively). Contrary to lipase activity, considerable pepsin activity was present in the antrum (18.17 +/- 4.12-23.07 +/- 5.60 U/mg protein). No difference in pepsin activities was found in the greater as compared to the lesser curvature. The data show similar origin and tissue distribution of gastric digestive enzymes in the suckling dog and human infant. The role of the newborn dog as an animal model for fat digestion in the human infant is discussed.