AbstractIn sheep, the gastrosplenic and mesenteric veins converge at an angle of about 140° to form the portal vein, which is joined, along its right ventral border, by the gastroduodenal vein. At the porta, right and left branches of the portal vein diverge at an angle of 65–70° to supply separate areas that join along a line between the fossa for the gall bladder, and the middle of the left branch. Right dorsal branches leave the portal vein or its right branch near the point of bifurcation.When131I‐albumin that had been heated was injected into the right ruminal vein and entered the portal stream in the gastrosplenic vein, no significant differences existed in the levels of radioactivity between the areas supplied by the different portal branches. When the131I‐albumin entered the portal stream from either the gastroduodenal or mesenteric veins, the area supplied by the right branch contained a significantly higher level of radioactivity than the remainder of the liver. When corrections were made for an unequal distribution of blood, it was found that blood from the gastrosplenic vein was distributed preferentially to the left branch, blood from the gastroduodenal vein to the right branch, and that blood from the mesenteric vein enters the right and left branches in preference to the right dorsal branches of the port