 At present, it is still unclear whether the properties of iPS cells are identical to those of hESCs. Initial data suggest that human iPS cells are indeed similar to hESCs in their phenotype, epigenetic status of pluripotent self-specific genes, telomerase activity, gene expression profile and in their capability to differentiate into progeny of the three germ layers both in vitro and in vivo in teratomas 2, 3, 5. In the mouse system, directed differentiation of iPS cells into bone marrow repopulating hematopoietic stem cells and functional dopaminergic neurons was demonstrated 6, 7. However, incomplete silencing of the constitutive expression of the transcription factors that were used to induce reprogramming can probably interfere with differentiation 1. Further studies are required to confirm that the developmental potential and biological properties of iPS cells are identical to hESC. 