Adding four factors only: Oct3/4, Sox2, c-Myc and Klf4, — to cultured fibroblasts leads to cell reprogramming. This method is effective for embryonal as well as for mature fibroblasts. The cells obtained are called induced pluripotent stem cell (iPS). They had morphology and proliferative ability peculiar to embryonal stem cells. Also, they expressed markers of embryonal stem cells. Subcutaneous introduction of iPS cells into mice provoked formation of neoplasms which contained spots of tissues derived from all three germ layers; iPS injected into mouse’s blastocytes took part in the formation of an embryo. Human iPS show numerous properties of embryonal stem cells: morphology, proliferative ability, surface antigens, epigenetic state of genes that are specific for the pluripotent state, telomerase activity. It was shown during in vitro and teratoma experiments that iPS could differentiate into cells of all three germ layers. In the in vitro experiments, factors necessary for reprogramming were delivered by retroviral vectors. Those vectors had the ability to integrate into genome that was fraught with carcinogenesis. In 2008, a mode was developed allowing to administer Oct3/4, Sox2, c-Myc and Klf4 into cells by means of cDNA. So scientists developed iPS which did not provoke formation of teratomas after they had been injected. The second factor increasing potential risk of neoplasm formation is с-Myc. To eliminate this problem, the scientists developed a method allowing to obtain iPS without using c-Myc. That method is less effective, but safer. Not only fibroblasts, but also liver and stomach cells may be used as the basis for iPS obtaining. Success of the experiments on mouse fibroblasts was lately reproduced in the experiments on human fibroblasts. Addition of the same four factors: Oct3/4, Sox2, c-Myc и Klf4, — led to iPS formation. Thus, it was the first time in 2007 when embryonal stem cells were obtained from somatic cells without using embryonal material.