The analysis of the experiments on somatic cloning of mammals reveals that possibly there is a group of cells whose nuclei have greater developmental potential than those of other cells. The group comprises cells of a particular developmental lineage, namely those originating from embryonic mesenchyme and mesoderm. The group remains to be elucidated if somatic cells effectively used for cloning are terminally differentiated, not yet fully differentiated or if they are stem cells. Developmental potential of somatic cell nuclei is best revealed when they are quiescent (i.e. in G0 phase of the cell cycle) upon being introduced into enucleated oocytes. The main obstacle in revealing the potencies of nuclei are the difficulties in their reprogramming before starting embryonic transcription, probably consisting in improper and not fast enough erasing of epigentic modifications of the genome. Developmental plasticity of whole cells as opposed to their nuclei has been experimentally presented in a particular class of somatic cells, namely in stem cells. Stem cells renewing a tissue of their origin can undergo transdifferentiation, that is, in atypical conditions they can differentiate into cells of other tissue and in chimaeras with early embryos - even into many diferent types of cells.