It is very little known that the molecular mechanisms control growth, cell differentiation, and invasion of ameloblastoma into bone. Tissue culture methods have also been used extensively for studies of the cell biology of ameloblastoma. The purpose of this study were to examined the ultrastructural features of ameloblastoma, and to apply these results to examine the pathogenesis of ameloblastoma in the future. Amelobalstoma was primarily cultured under 0.1, 0.15 and 1.2mM Ca++ of KBM bullet kit at 370C and 5% C02. For transmission electronmicroscopy(TEM), cultured ameloblastoma cells were immediately fixed in 2.0% glutaraldehyde in O.lM cacodylate buffer(pH 7.4) at 40C for 1h The ultrathin sections were stained with uranyl acetate and lead citrate, and examined by TEM. The obtained results were as follows. Primay culture ameloblastoma grown in 0.1 mM Ca++ showed interlacing papillary projections without desmosome within early passage(3-4). Primary culture amelobalstoma under high calcium showed prominent desmosomes or tight junctions within early passage. There was evidence of cellular degeneration, as exemplified by nuclear pyknosis, the margination and clumping of the chromatin, and vaculolation under high calcium. The sparse ribosomes, the cytoplasmic space filled with vacuoles, and the condensed mitochondria were seen under high calcium. From the aboving results, under high calcium primary culture ameloblastoma showed rapid cellular degeneration within early passage, indicating that the cells were gradually losing metabolíc actívitíes, leading to enventual cell death. It was thought that it would be necessary to establish cultured immortalized amelobalstoma cell line for studying the pathogenesis of odontogenic tumors.