Using light microscope (LM) and scanning electron microscope (SEM) a study of the surface morphology of rat oral epithelium was undertaken. A good correlation was found between the LM and SEM findings in the demonstration of the characteristic differences in surface structure between completely and incompletely orthokeratinized areas of the rat oral epithelium. Completely keratinized epithelium (hard palate and attached gingiva) shows a surface layer of orderly arranged, closely approximated and overlapping cells. The individual cell surface shows a honeycomb pattern of interconnecting ridges surrounding depressions or micropits. Incompletely keratinized epithelium (buccal mucosa, alveolar sulci, gingival crest and interpapillary area of the dorsum of the tongue) shows a very uneven, corrugated surface layer. There is considerable loss of cell cohesion with the formation of wide intercellular clefts. The individual cell surface is characterized by microplications of irregular size and arrangement. The findings of the present investigation are discussed in the light of an idea previously put forward by the authors that a correlation exists between surface morphology of the keratinized rat oral mucosa and colonization and penetration of Candida organisms in experimental candidosis.