Recent work has prompted a dramatic shift in thinking about cell regeneration, as researchers have come to appreciate the ability of adult stem cells to adopt the fates of many cell types, not just those in a particular tissue or a specific developmental lineage. The Verfaillie laboratory has shown that multipotent adult progenitor cells (MAPCs), a marrow-derived stem cell type with an impressive developmental repertoire, can be prepared from humans or rodents and can be used to reconstitute cells of all embryonic lineages when injected into a blastocyst. Technically more demanding but also more useful if the hope is to develop therapeutic engraftment techniques using autologous cells is the ability to generate uniform populations of a desired cell type ex vivo. Verfaillie's group has found that a single MAPC can be passaged for many cell divisions in an undifferentiated state or can be induced to differentiate along any of several paths, yielding angioblasts, muscle cells, or neurons, among other cell types. Whether cultured MAPCs can also generate epithelia has been uncertain, but Schwartz et al. now show that, by providing specific soluble factors and a suitable microenvironment, they can drive MAPCs to form hepatocytes. The resulting cells express albumin and other characteristic hepatocyte proteins, and they can store glycogen and adopt a normal, polarized morphology. As Schwartz et al. caution, it remains unclear whether the undisturbed marrow of healthy animals contains any single stem cell type with the developmental plasticity of MAPCs-- a caveat that might be applied to much of current stem cell research.