The BCR/ABL preleukemic fusion gene (PFG) is one of the most frequent fusion genes in acute lymphoblastic leukemia (ALL) and was also detected in hematopoietic cells from umbilical cord blood (UCB) of healthy newborns. Since hematopoietic stem/progenitor cells (HSPC) are considered to be a critical cellular target for origination of leukemia, we have studied the presence of BCR/ABL PFG in expanded subpopulations of HSPC and differentiated cells from UCB of those healthy newborns, who have previously been tested positive for BCR/ABL by screening of their UCB mononuclear cells using RT-qPCR and FISH methods. We isolated cells from human UCB samples positive for BCR/ABL and negative controls. The isolated cells were sorted into 5 hematopoietic and progenitor cell subpopulations. We analyzed BCR/ABL in sorted and expanded subpopulations of UCB using FISH and RT-qPCR. We found that the number of BCR/ABL positive cells was similar in each studied subpopulation and the same as in differentiated lymphocytes. Our data showed that there is no specific subpopulation of hematopoietic and progenitor stem cells with an increased leukemogenic potential due to the presence of higher copies of BCR/ABL.