Liver tissue from 12 different mammalian species was studied with a fluorescence histochemical technique for the cellular localization of amines (Falck-Hillarp technique) and with a chemical method for the determination of norepinephrine (HPLC-technique). Adrenergic nerve plexus were found in interlobular blood vessels derived from the portal vein and hepatic artery. Varicose adrenergic nerve fibres were, generally, seen to branch from the fibres around the blood vessels and to enter the liver parenchyma, where they formed a randomly distributed intralobular network. The density of these intralobular fibres showed marked species variation. Human liver and liver from the rhesus monkey, baboon, cynomolgus monkey and guinea pig showed a high density of parenchymal adrenergic nerves. Rabbit, cat, pig, cow and horse liver formed an intermediate group, having fewer varicose adrenergic nerve fibres but an unequivocal distribution of these nerves to the liver parenchyma. In rat and mouse liver no parenchymal innervation could be demonstrated. The density of the parenchymal innervation generally correlated with the concentration of norepinephrine in the liver tissue.