We used 2.15 to 2.3% collodion in amyl acetate to form a replica of the corneal surface epithelium in vivo in seven rabbit eyes and ten human eyes. When it was peeled off the replica removed superficial epithelial cells in patches. The corneal epithelium regenerated within one week. Repeated applications at weekly intervals for three months produced no harmful long-term effects in five rabbit corneas as evaluated with slit-lamp biomicroscopy, histological methods, and vital staining of the endothelium. In ten human eyes, the technique was harmless and chemically cauterized the dendritic herpetic ulcers. We studied the replicas and cells by conventional histological methods and electron microscopy. The preservation of cells was fairly good even for ultrastructural study.