Fetal membranes of early human pregnancy were investigated by a simple method in which surface ultrastructure could be evaluated rapidly. The differentiation of amniotic epithelium was found as early as the twelfth week of pregnancy. Plaque-like cell groups with morphologic features in common with free cells in amniotic fluid were seen in the epithelium, probably constituting the source of these cells. The microvillous abundance on chorion villi and the spatial interrelations of microvilli were particularly studied. The morphologic findings are related to earlier suggestions concerning function and to earlier transmission electron microscope results.