The canals of Hering and bile ductules in human liver contain hepatic progenitor cells that can differentiate towards the biliary and hepatocytic lineage. Proliferation and differentiation of hepatic progenitor cells is referred to as ‘activation’ and this process occurs to a variable degree in almost all human liver diseases. Several studies indicate that hepatic progenitor cell activation in diseased liver is regulated by neural and neuroendocrine factors such as the vagal innervation. Analogous to oval cells in animal liver, there is evidence that human hepatic progenitor cells may be able to give rise to hepatocellular carcinoma and other liver tumors.