In this article, the development and application of a modified technique of impression cytology for the electron-microscopic examination of corneal epithelium is presented. Corneal epithelium of controls and diabetic patients was obtained using millipore filters, which had been presoaked with EDTA to weaken intercellular adhesions. Light and electron microscopy (EM) of the control samples showed sheets of well-preserved corneal epithelial cells. Therefore, this modified technique is supposed to be useful for the analysis of alterations of the corneal epithelium. EM of corneal cells of diabetic patients showed irregularly formed epithelial cells. The corneal epithelium of diabetic patients revealed thickening of the basement membrane and a decreased number of hemidesmosomes. The alterations observed in specimens of diabetic patients represent the morphological equivalent of an impaired epithelial barrier function, an increased fragility of epithelial lining and the disturbed healing properties occurring in diabetic keratopathy.