Diversion of portal venous blood into the systemic circulation is associated with a high incidence of peptic ulcer in man.1Gastric secretory levels in patients with portacaval shunts are not above normal, but are probably elevated from preoperative values.2In the dog, portacaval shunting definitely enhances the rate of acid secretion by the stomach.3This has been shown to be due to a circulating substance, probably histamine.4 The purpose of the present study was to determine, in the dog, changes in gastric, duodenal, pancreatic, and esophageal blood flows following creation of portacaval shunts. The radioisotope (42K or86Rb) distribution method was used to measure tissue blood flows. Materials and Methods End-to-side portacaval anastomoses were constructed in nine healthy mongrel dogs. The control group consisted of 13 normal animals that had undergone no operation. All dogs were fed a standard diet of commercial dry cereal