Abstract: Described herein is a method of expanding human hepatocytes in vivo using an immunodeficient mouse which is further deficient in fumarylacetoacetate hydrolase (Fah). The method comprises transplanting human hepatocytes into the immunodeficient and Fah-deficient mice, administering an IL-1R antagonist to the mouse and allowing the hepatocytes to expand. Alternatively, the method includes transplanting human hepatocytes into the immunodeficient and Fah-deficient mice, wherein the mouse is further deficient for IL-1R and allowing the hepatocytes to expand. The method also allows serial transplantation of the human hepatocytes into secondary, tertiary, quaternary or additional mice.