Detectable levels of gastrin are present in the canine fetal antrum as early as the fourth week before birth. The mean concentration of full-thickness antral gastrin is significantly greater in pups older than six weeks of age than in pups less than six weeks of age. The mean gastrin concentration of antral mucosa in pups six to nine weeks and 9- to 12-weeks old was not significantly different from that in canine fetuses. The antral gastrin concentration is strongly correlated with the serum gastrin concentration in pups (8 to 12 weeks old) but only weakly correlated in adult dogs. Parietal cells are present in the canine fundus as early as the fourth week prior to birth.