Since the trophoblast-uterine adhesion is as nearly a universal phenomenon in implantation as can be found, an attempt was made to determine whether or not there was a reduction in cell surface glycoproteins in the rat, as can be observed in the ferret. Neither colloidal iron nor cationized ferritin revealed the type of pattern anticipated for a localized reduction in surface negativity in the imprint of the blastocyst in the implantation chamber. The use of lectin-coated latex beads also proved disappointing in defining regional differences in adhesiveness. However, a number of observations on the changing shape of the implantation chamber, the secretion of periluminal material by decidual cells, and the penetration of the residual basal lamina of the luminal epithelium by the decidual cells were made in the course of these studies. The implantation chamber of the rabbit, in which the blastocyst does not make an imprint, was contrasted with that of the rat. The areas of fusion of trophoblast knobs with uterin epithelial cells shown to be visible by scanning electron microscopy. Finally, some observations on the hypertrophy of maternal epithelial cells to form the uterine plaque in the rhesus monkey are described, and the hypertrophy of endothelial cells to form admirably suited to protein secretion is presented.