The results of our previous studies in which we used the so-called strategy . chemotactic isolation to stromal - derived factor 1 ( called Stromal Cell Derived Factor 1 , SDF- 1 ) in combination with the technique of real-time PCR (Real Time PCR , RT- PCR) showed that there is a bone marrow cell population expressing CXCR4 + mRNA markers for early stem cells targeted tissue ( UTKM ) . The paper will be presented the results of research showing that CXCR4 + UTKM : 1 ) present in the bone marrow of young animals , and then the number decreases with age, 2 ) belong to the fraction of cells niehematopoetycznych bone marrow phenotype Sca - 1 + CD45 - , 3 ) are enriched in cells expressing embryonic / pluripotent transcription factors ( Oct-4 , Nanog , and Rex- 1 ), 4) are stress-induced , or by using G - CSF mobilized peripheral blood , where it can then migrate to the gradient of SDF- 1 released by damaged tissues , 5) may be involved in the regeneration of tissues / organs. Taking these observations into account we postulate that the bone marrow is not only a source of hematopoietic stem cells ( KKM ), but also includes CXCR4 + UTKM . The presence of these cells in the bone marrow must be taken into account when analyzing the results interpreted as the ability to transdifferentiation KKM / plasticity. Since, as shown, the population of CXCR4 + UTKM embryonic expresses a number of transcription factors , it may comprise a more primitive pluripotent stem cells ( PKM ) . The fact that UTKM the highest percentage in the bone marrow are juveniles, and their number decreases as they age may in turn explain why the regeneration processes are becoming less effective in older animals .