Corneal buttons were cut from cat and human donor eyes by anterior trephination (with or without scissor completion) and from excised corneoscleral rims by posterior trephination (with or without a press). Scanning electron microscopy was used to evaluate the slope and quality of the cut edge, the diameter of the section of Descemet's membrane that was actually cut, and the loss of endothelial cells around the cut edge. With anterior trephination, the diameter of the section of Descemet's membrane that is cut was found to be less than that of the trephine because the cut edge slopes inward. Posterior trephination with or without a press consistently produced circular buttons with accurately cut outward-sloping edges. This resulted in a diameter of Descemet's membrane which was greater than in the anteriorly trephinated buttons. There also was less damage to peripheral Descemet's membrane and endothelium with the posterior method, especially when compared to scissor cut buttons. A 360 degree peripheral ring of Descemet's membrnae (0.05 to 0.28 mm in width) was denuded of endothelial cells with all techniques.