In the vagina of women at the reproductive age, more than 170 strains of bacteria and yeasts are found. The effect of vaginal flora on neonatal T cells is yet to be investigated. We analyzed CD45RA and CD45RO expression on neonatal CD4+ T cells and cytokine production in CBMC cultures (interferon-gamma (IFN-gamma ), interleukin-4 (IL-4) and IL-12) related to vaginal bacteria isolated from a maternal vagina. We collected vaginal swabs from 36 women at the first stage of the delivery and cord blood from their newborns. IFN-gamma, IL-4, and IL-12 in stimulated CBMC were measured and the expression of CD45RA/CD45RO on CD4+ T cells was assessed. We noted the difference in CD45RO CD4+ expression and IL-12 levels between the newborns whose mothers were or were not colonized with Lactobacillus in the vagina (newborns whose mothers were colonized with Lactobacillus: CD45RO-10%+/-3; IL-12-0.2 pg/mL +/- 0.05; newborns whose mothers were not colonized with Lactobacillus: CD45RO-6%+/-3; IL-12-2.0 pg/mL +/- 0.7). Our results may indicate that lactobacilli in maternal vagina influence the development of neonatal immune system. Yet, more research is needed using specified bacterial antigens.