AbstractThe portal vein in the rabbit is formed by union of the gastrosplenic vein, which extends caudally and to the right, and the relatively larger and cranially directed mesenteric vein, formed from cranial and caudal mesenteric and caudal pancreaticoduodenal tributaries. The gastroduodenal vein, which receives blood from the distal pylorus, greater omentum, pancreas and duodenum, joins the rabbit portal vein opposite the branch to the caudate lobe. In the cat, the portal vein is formed by the junction of the gastrosplenic, which is directed transversely or cranially, and the mesenteric, and receives two main tributaries: the gastroduodenal, which is the main vein from the stomach, and the cranial pancreaticoduodenal.When 131I‐rose bengal was injected into the spleen of conscious standing cats and entered the portal vein in the gastrosplenic, it was distributed preferentially to the right branch and the left lateral ramus of the left branch. In the rabbit, there was no evidence for preferential distribution of splenic blood, but blood from the cranial mesenteric vein was distributed preferentially to the right and caudate branches and that from the caudal mesenteric to the caudate. This distribution was affected by the entry of blood in the gastrosplenic vein. Although statistically significant differences did occur in the intrahepatic distribution of blood derived from the portal tributaries, the absolute differences were small.