Exfoliative cytologic findings of the oral mucosa in three cases of Acatalasemia (Takahara's disease) were investigated by means of Papanicolaou's method. Three cases were sisters of the same family, 19, 22, and 15 years of age. Oroantral fistula was noticed in the left molar area in Case 2 and Case 3 complained of loosening of anterior lower teeth with marginal gingivitis in the left lower molar ares. Smears were prepared by the following technics: 1) Scraping four different areas of the oral mucosa---hard palate, gingiva, radix linguae and buccal mucosa without causing bleeding. 2) Sediment taken from centrifuged mouth washings by physiologic saline solution. 3) Cells caught by membrane filter or both of them. All the smears were stained by Papanicolaou's technic and histologic examination of the gingiva was made in comparison with cytologic smears in Case 3. Thus keratinization of the epithelial cells were studied. 1) Keratinizing tendency was the same as those of normal mucosa in Cases 1 and 3. In the ulcerating area of Case 3 keratinized cells showed an increase as healing was going on, while they showed a marked decrease in Case 2, which might be due to the decrease of local resitance associated with ulcerative changes and the influence of partial denture. 2) Exfoliated cells of the whole oral mucosa in case of mouth washings Cases 1 and 3 showed the same findings as normal cases and Case 2 showed a marked decrease of keratinized cells. These findings were same as those of four different areas of the oral mucosa. 3) Gingiva of Case 3 showed little difference from normal mucosa in histopathologic findings.