The regional blood flow of the dog's stomach and upper part of the duodenum is measured by radioactive microspheres. A complete surgical interruption of vascular connections between antrum and corpus changes blood flow distribution, as measured 2 weeks after operation. We find a significant fall of flow to the mucosa of the corpus and the muscular layer of the antrum. Mucosa and muscularis of the canine stomach are supplied by different sources: The arteries of the muscularis, which show extramural origin, are mainly supplied by the left gastric vessels. The gastric mucosa--even of the corpus--shows main blood supply from the arteries of the gastroduodenal region. Gastric secretion shows normal response on stimulation by Pentagastrin. Thus an accidental vagotomy is excluded as a possible cause of the registered flow changes. The effect of Pentagastrin on the gastroduodenal circulation is interpreted an an occlusion of arteriovenous shunts.