Ameloblastomas are benign odontogenic tumor and the most common neoplasm in jaws and they have locally invasive property and high recurrence rate. Four typical subtypes ameloblastomas are plexiform, follicular, granular cell and acanthomatous type, but their developmental states during tumorigenesis are uncertain. And thus authors studied about developing states of four types of ameloblastomas by immunohistochemical staining for cytokeratin 8/18 which was an intermediate filament of epithelial cell origin and for vimentin which was an intermediate filament of mesenchymal cell origin, and then by comparative analyses of the results. Authors selected seven cases for every four types of ameloblastomas, and then performed immunohistochemcial staining for cytkeratin 8/18 and vimentin to all selected specimen by using monoclonal antibodies about cytoleratin 8/18 and vimentin, LSAB(Labelled StreptoAvidin Biotin) reactant and HRP(Horse Radish Peroxidase) system. Labelling indices of cytokeratin 8/18 of plexiform and follicular types of ameloblastomas were significantly high values in the group of ameloblast-like cells and labelling indices of cytokeratin 8/18 of all types of ameloblastoma were high values in the group of transformed cells, but their differences were not significant. Labelling index of vimentin of plexiform ameloblastoma was significantly high value in the group of ameloblast-like cells and others showed comparatively lower values. Labelling index of vimentin of granular cell type of ameloblastoma in the group of transformed cells was significantly high value and others showed comparatively lower values. Consequently the most primitive form of ameloblastoma was plexiform, and more differenciated form was follicular type and granular cell type and acanthomatous type were most differenciated form of ameloblastomas