Studies on some enzyme activities as measured histochemically in the ligated common bile duct rat liver are reported. They show principally: an increased GGT reaction in the neoductular cells; a diffusion of the LAP reaction to the neoductuli; an immediate increase and diffusion of the alkaline phosphatase reaction; an increase of G-6-PA and AMPA reactions; an increase, during the first week, of the Phyla activity and a contemporary decrease of the UDPG-GS reaction. No significant changes have been observed in other enzyme activities. By means of some dehydrogenase reactions, morphological evidence that the hepatocytes may be involved in neoductular cells formation was obtained.