 Currently, retroviral vectors are most commonly used to introduce and express the transgenes which reprogram the somatic nucleus 1-5. The use of retroviral vectors, which integrate into the host cell genome, may cause hazardous insertion mutagenesis. Moreover, the use of potentially oncogenic transcription factors, such as c-Myc, significantly limits the clinical use of human iPS cells for future cell therapy. However, successful derivation of iPS cells was demonstrated without the forced expression of c-Myc. The decreased efficiency of reprogramming, in the absence of overexpressed c-Myc, may be improved by molecules which act via epigenetic mechanisms. Moreover, successful derivation of iPS cells was recently reported with the use of non-integrating adeno viral vectors or repeated transfections. Thus it appears that with further developments, it may be possible in the future to safely induce pluripotent cells from somatic cells for therapeutic applications. 