The most controversial problem in the present biology and medicine is the existence of stem cell plasticity. Experimental biology and medicine have been working with stem cells and stem cell therapy more than twenty years. The term plasticity, as it is understood, is the potential of stem cell phenotypes that is much broader that phenotypes of differentiated cells of their original tissues. Many laboratories have documented the existence of stem cell plasticity; however, many objections to the reported results still exist. Here, we present some of these objections questioning the data on stem cell plasticity. We wish to point out some problems associated with plasticity of stem cells, transdifferentiation and cell fusion. Recent experimental results indicate that stem cells may have a key role in stem cell therapy. This review is an introductory discussion on the stem cell plasticity and stem cell therapy.

        Key words: stem cells, plasticity, transdifferentiation, stem cell therapy.