The aim of this study was to estimate the populations of peripheral blood myeloid and lymphoid dendritic cells (CD1c(+), BDCA-2(+), BDCA-4(+)) and the CD1c(+):BDCA-2(+) ratio in phases of the ovarian cycle and in normal pregnant patients. 18 non-pregnant women and 17 normal pregnant women were included. Dendritic cells were isolated from peripheral blood, stained with monoclonal antibodies (mAbs) against blood dendritic cell antigens (anti-BDCA-1, BDCA-2, BDCA-4) and estimated using flow cytometry. CD1c(+), BDCA-2(+) and BDCA-4(+) dendritic cells were present in the follicular and luteal phases of the ovarian cycle and in all trimesters of normal pregnancy. The percentages of CD1c(+) dendritic cells did not differ between the follicular and luteal phases of the ovarian cycle. The percentage of BDCA-2(+) dendritic cells was lower in the luteal phase of the ovarian cycle compared with the follicular phase, but the differences were not statistically significant. The CD1c(+):BDCA-2(+) cell ratio was significantly lower in the luteal phase compared with the follicular phase of the ovarian cycle. The numbers of dendritic cells were significantly lower in the second trimester when compared with the first and third trimesters of normal pregnancy. Furthermore, in the second trimester, the CD1c(+):BDCA-2(+) ratio was higher than in the other trimesters of normal pregnancy. All populations of dendritic cells and the CD1c(+):BDCA-2(+) ratio did not differ in the first and third trimesters of physiological pregnancy. Our results suggest that myeloid and lymphoid dendritic cells are not affected by steroid hormones during the menstrual cycle. The deficiency of peripheral blood dendritic cells observed during the second trimester of normal pregnancy can be associated with their migration to the uterus during the second physiological invasion by cytotrophoblast.