Phase-contrast studies on amnion cells in suspension following trypsinization of membranes showed the cells to be usually markedly vacuolated and highly refractile and the nucleus to be obscured; a few cells were non-vacuolated, dark, and smaller. Studies were initiated to determine the origin of the small dark cells and their growth in cell culture, utilizing a series of staining technics to elaborate the differences seen by phase-contrast microscopy.Biopsies of amniotic membranes from Caesarian sections more frequently showed less vacuolation of epithelium as compared to amnions from normal deliveries, which were usually markedly vacuolated; trypsinization of membranes made up of non-vacuolated epithelium yielded suspensions made up entirely of smaller, dark cells. Studies on the process of cell separation showed this change of the non-vacuolated cells to smaller dark cells to be an effect of trypsin. The small dark cells were superior to the vacuolated cells for culture purposes.