The contribution of the vagus nerves to the innervation of the liver has been studied with the cobaltous chloride impregnation method. With this method we have demonstrated that the fiber plexus in the rat hepatic parenchyma, that we had previously described and stained for acetylcholinesterase, is of a nervous nature and of vagal origin. Our results show that branches from the vagus spread abundantly with the connective tissue at the capsule. From this peripheral location, the fibres expand deeply through the parenchyma in close contact with the hepatocytes towards the central veins. Other branches run with the interlobular connective tissue, distributing to the portal veins, hepatic arteries and biliary ducts. They also have lateral branches which penetrate into the parenchyma.