Induced pluripotent stem (iPS) cells have generated keen interest/ndue to their potential use in regenerative medicine. They have/nbeen obtained from various cell types of both mice and humans by/nexogenous delivery of different combinations of Oct4, Sox2, Klf4,/nc-Myc, Nanog, and Lin28. The delivery of these transcription factors/nhas mostly entailed the use of integrating viral vectors (retroviruses/nor lentiviruses), carrying the risk of both insertional mutagenesis/nand oncogenesis due to misexpression of these exogenous/nfactors. Therefore, obtaining iPS cells that do not carry integrated/ntransgene sequences is an important prerequisite for their eventual/ntherapeutic use. Here we report the generation of iPS cell lines/nfrom mouse embryonic fibroblasts with no evidence of integration/nof the reprogramming vector in their genome, achieved by nucleofection/nof a polycistronic construct coexpressing Oct4, Sox2, Klf4,/nand c-Myc