The surface of the cornea of rabbit eyes was studied under the scanning and transmission electron microscope, and was compared with the pathological changes which occurred after experimental UV irradiation. Both methods showed two types of cells: (1) cells rich in microvilli, containing an active karyoplasm and cytoplasm structure, and (2) smooth-surfaced cells with perhaps a few microvilli whose karyoplasm and cytoplasm are in a state of liquefication and whose membranes are defective. After U V irradiation, the microvilli were destroyed, and the second cell type was shed. The regeneration of the first cell type leads to a new formation of the microvilli from the centre of the cell, whereby tonque-like smooth processes can be seen at the periphery. These results support the thesis of the function-dependent formation of the microvilli and the age-dependent functional efficiency of the top layer of corneal, epithelial cells.