In severe injury, liver-cell progenitors may play a role in recovery, proliferating, and subsequently differentiating into mature liver cells. Identifying these progenitors has major therapeutic potential for ex vivo pharmaceutical testing, bioartificial liver support, tissue engineering and gene therapy protocols. Potential liver-cell progenitors have been identified from bone marrow, peripheral blood, cord blood, foetal liver, adult liver and embryonic stem cells. Differences and similarities are found among cells isolated from rodents and humans. This review will discuss identifying markers and differentiation potential in in vitro and in vivo models of these putative progenitors in both humans and rodents.