By transmission electron microscopic examination, intracellular and extracellular deposits of a fibrillogranular material were detected in the stroma, Descemet membrane, and endothelium in the donor and the host cornea. Additionally, numerous electron-lucent lacunae and vacuoles could be observed in the stroma and posterior nonbanded portion of Descemet membrane. In the host cornea, a marked loss of keratocytes with occasional large, swollen keratocytes completely filled with fibrillogranular inclusions was observed, whereas in the donor cornea, a normal number of keratocytes with signs of increased secretory activity was present (Figure 3, A through F). There was evidence of invasion of some large, diseased host keratocytes into the donor button in the pre–Descemet membrane stroma near the interface. Alterations of posterior Descemet membrane, including fibrillogranular deposits, electron-lucent lacunae, abnormal collagen fibers, and guttae formation, were more prominent in the host cornea.