Rodent bone marrow cells can contribute to liver. If these findings are applicable to humans, marrow stem cells could theoretically be harvested from a patient and used to repair his/her damaged liver. To explore this potential, CD34(+) or highly purified CD34(+)CD38(-)CD7(-) human hematopoietic stem cells from umbilical cord blood and bone marrow were transplanted into immunodeficient mice. One month after transplantation, carbon tetrachloride (CCl(4)) was administered into the mice to induce liver damage and hepatocyte proliferation. Mice were analyzed in comparison with CCl(4)-injured mice that did not receive transplants and noninjured controls that received transplants with the same stem cell populations, one month after liver damage. Human-specific albumin mRNA and protein were expressed in the mouse liver and human albumin was detected in the serum of mice that had received CCl(4) injury. Human alpha-fetoprotein was never expressed, but in some mice, human cytokeratin 19 was expressed, which may indicate bile duct development in addition to the albumin-secreting hepatocyte-like cells. Human albumin was not expressed in the starting stem cell populations in injured mice that did not receive transplants nor in noninjured mice that had received transplants of human stem cells. Human albumin expression was detected only in CCl(4)-treated mice that received transplants of human stem cells, and recovery was increased by administration of human hepatocyte growth factor 48 hours after the CCl(4)-mediated liver injury. Our studies provide evidence that human "hematopoietic" stem/progenitor cell populations have the capacity to respond to the injured liver microenvironment by inducing albumin expression.