We investigated the kinetics of nucleated cells and CD34+ cells to determine the differences between cord blood (CB) and neonatal peripheral blood (NB). The correlation coefficient between white blood cell (WBC) counts and neutrophil counts was statistically significant for CB and NB at 0, 24, and 48 hours postnatally. There were no differences in the absolute counts of lymphocytes, CD3+ cells, and CD19+ cells; however, the CD16/56+ cell counts for CB were significantly decreased 48 hours postnatally (P = .011). The number of GM-CFU counts (P = .02) and CD34(+) cells (P = .049) as well as CD34+CXCR4+ cells (P = .002), CD34+CD49d+ cells (P = .001), and CD34+CD44+ cells (P = .001) in CB were significantly increased over those of NB at delivery, and the numbers decreased gradually until 48 hours after delivery. In conclusion, the change in WBC count several days after delivery were closely associated with a temporary increase in neutrophils, and NK cells significantly decreased over time postdelivery. In addition, CD34+ cells were more prevalent in CB than in NB, and gradually decreased after birth. Such a change might be directly related to the kinetic changes of CXCR4 or CD49d and CD44 expression on CD34+ cells in CB and NB.