Special materials were collected from medical abortions at 6 to 11 weeks' gestation (19 cases + 5 amputated uteri), late abortions at 24 to 25 weeks' gestation (n=5) + 4 uteri and biopsies of the placental bed and uterus during the third trimester for the morphometric evaluation of the cell composition of cytotrophoblast invasion into the uteroplacental area. The interstitial cytotrophoblast (IC) and multinucleated giant cells (MGCs) immunovisualized by cytokeratin 8 were determined in the standard field of view (area 785,000 µm). The maximum IC distribution frequency that was 15-17 times greater than that for MGCs was found during the first trimester of apparently normal pregnancy. These cells' diameters measured in the nuclear cross section were 12-20 µm for IC and 22-28 µm for MGCs. In the mid-gestation (22-25 weeks), the distribution frequency of IC remained high (200-208 cells); it drastically fell to 86-100 cells at 31 weeks and to 27 cells with a tendency for increasing the diameter up to 24 µm in the full-term period. On the contrary, MGCs gradually increased their distribution frequency (from 14 cells at the end of the first trimester to 52 cells in the full-term period). These data characterize the cellular ratios of cytotrophoblast invasion during apparently uncomplicated pregnancy. They are important as the first step for the morphometry of an invasive process in different obstetric abnormalities.