Totally 25 cases without any fetal anomaly, 10 with polyhydramnios, 10 with oligohydramnios and 5 with normal volume of amniotic fluid were taken into consideration. Their amnion covering the placenta and umbilical cord were examined under electron microscope. In the group with polyhydramnios the microvilli facing the amniotic cavity were denser in certain regions. The intercellular space was widened and the terminal bars were opened. Within the cells the number of vesicles were increased and there were large cysternas within these vesicles. It was postulated that the large cysternas found in the basal and apical parts of the cell were composed of macropinocytosic vesicles of the basal membran. In the group with oligohydramnios the microvilli on the apical side were diminished. The intercellular space of the lateral side was narrowed. The electron density of the basal lamina was increased. The cellular structures were apparently reduced having just a few vesicles and lipid granules. Both in polyhydramnios and oligohydramnios the amniotic epithel cells covering the placenta and umbilical cord are responsible for the transfer of the fluid into the amniotic cavity. Possibly they control the amount of fluid by reducing or increasing its passage
