Gene and stem cell therapies hold promise for the treatment of a wide variety of inherited and acquired human diseases. Identification of genes involved in human disease and development of novel vectors and devices for delivering therapeutic genes to different tissues in vivo have resulted in significant progress in the area of gene therapy. Isolation of stem cells from organs formerly thought to have no regenerative potential, the demonstration of stem cell plasticity, and the creation of human embryonic stem cells clearly demonstrate the feasibility of human stem cell therapy. Much additional work remains to be done in the areas of vector development and stem cell biology before the full therapeutic potential of these approaches can be realized. Of equal importance, the ethical issues surrounding gene- and cell-based therapies must be confronted.