There have been many reports on the histopathologic characteristics of laryngeal polyp. Recently, many authors have concentrated on the phono-trauma theory that the evolution of a laryngeal polyp might be due to increased hyperemia of vocal fold with vasodilation as a possible pathogenesis. The histopathology of the laryngeal polyps show various changes in the subepithelial tissue and the epithelial layer. Therefore, to support this therory, it is necessary to define whether the differentiation of the epithelium of the laryngeal polyp is similar to that of normal vocal fold or not. To evaluate the differences of the reaction patterns of lysozyme, factor VIII and the subtype of cytokeratin expression between the laryngeal polyps and the normal vocal folds, we analyzed the paraffin-embedded tissues of 11 cases of laryngeal polyp and 3 cases of normal vocal fold obtained at surgery by the immunohistochemical technique using two prediluted polyclonal antibodies of lysozyme and factor VIII, and five prediluted antiepithelial monoclonal antibodies. The results were as follows : 1) There were no difference of lysozyme expression between normal vocal folds and laryngeal polyps, so it seemed that the serous gland did not attribute to the pathogenesis of the laryngeal polyp. 2) The factor VIII expression of the laryngeal polyps showed that the degenerative changes of vasculature in subepithelial layer attributed to the pathogenesis of the laryngeal polyp. 3) The reactive patterns of cytokeratin expression of the laryngeal polys showed the transtional patterns from non-keratinized stratified squamous epithelium to keratinized epithelium, and were similar to that of normal vocal folds. In conclusion, it seemed that the laryngeal polyp evoluated from the primary change of the subepithelial layer such as the degenerative change of vasculature and infiltration of inflammatory cells, and the secondary change of the epithelial layer such as hyperplasia, hyperkeratosis, acanthosis and atrophy and so on. So our histopathologic and immunohistopathologic data might be one of the evidence that support the phono-trauma theory.