Considering the revolutionary potential of adult stem cells, the search for adult liver stem cells has been ongoing for many years. Given the tremendous ability of the liver to regenerate and the discovery of adult stem cells in many organs of the body (e.g., skin, bone marrow, intestine), one might assume that this regenerative capacity is attributable to stem cells in the liver. However, the existence of such cells was critically questioned as recently as 20 years ago and there has been difficulty in isolating and characterizing such cells in the liver. It is believed this regenerative capacity results from the ability of hepatocytes to replace themselves after injury or death (compensatory hyperplasia). Study of liver injury, regeneration, and carcinogenesis in rodent models has provided ...