The influence of acidification of the duodenal contents, of intravenous secretin, cholecystokinin and pancreozym injections on hepatic (HAF) and left gastric artery (GAF) and on portal vein blood flow (PVF), bile and pancreatic juice output was studied in dogs. Acid introduction into the duodenum increased HAF and PVF by 20 and 25 percent, respectively. GAF did not change significantly. Secretin and cholecystokinin also increased PVF by 25 percent but HAF changes were less than after acidification. Pancreozym increased significantly only HAF. There were also differences between the effects of duodenal acidification and of the individual hormones on bile and pancreatic juice excretion. It is concluded, that splanchnic circulatory changes observed following duodenal acidification are not produced by the action of a single intestinal hormone but are due to the interplay of several factors.