Intrahepatic biliary cell plasticity was investigated in a rat model that combined prior bile ductular cell hyperplasia after bile duct ligation with subsequent CCl4-induced hepatonecrosis. Morphometric analysis of histologic liver sections from rats at 4 to 6 weeks after bile duct ligation and 3 to 5 days after CCl4 demonstrated the total section area to be occupied by near-equal amounts of hyperplastic bile ductular tissue area and hepatonecrotic area. Of particular significance was the unique presence, albeit infrequent, of newly appearing hepatic cell cholangioles composed of both biliary epithelial cells and one or more 'ductular hepatocytes' exclusively within the hyperplastic bile ductular tissue area of liver sections from the bile-duct-ligated/CCl4-treated rats, but not observed in control liver sections. This finding is compatible with the possibility of a 'transdifferentiation' of some hyperplastic biliary epithelial cells into 'ductular hepatocytes' in response to an extreme hepatic injury.