Greyish-white spots, varying in size, caused diagnostic problems in 2 patients with pre-invasive corneal carcinoma. Keratectomy specimens permitting light and electron microscopy indicated that the smaller spots predominating in one patient correlated with epithelial microcysts and vacuoles, while areas of parakeratosis accounted for the macroscopic white patches found in the other. A variety of ultrastructural abnormalities, including excessive basement membrane fibrillogenesis, were present in both cases.