Biopsy was taken from the gingivae in 42 cases of pericoronitis and 8 normal healthy control cases, which were the same materials used in previous cytologic study. Sections were stained by Hematoxylin-Eosin, Azan and Papanicolaou methods, investigated histopathologically and compared with the findings of exfoliative cytology. 1) In normal gingivae keratinous layer could be seen in various degrees, while in acute inflammatory ones typical keratinous layer could not be observed and keratinization showed a decrease. 2) In Azan and Papanicolaou stainings yellow and red stainings decreased in the superficial layer and a definite correlation could be seen between keratinization and staining effect according to structural density of the tissue. Findings of exfoliative cytology and histo-pathology were completely agreed in their comaprison. 3) The SH groups of the surrounding tissue in case of pericoronitis were investigated by Chévremout-Erédéricq's reaction but a decisive conclusion could not be drawn from these results. It could be concluded that pericoronitis was induced by infection of the dental follicle after tooth eruption and could be divided into acute and chronic types clinically. As the results obtained from exfoliated epithelial cells classified according to their staining effect of the cytoplasm by Papanicolaou staining, a considerable decrease of keratinization could be noticed in cases of pericoronitis in comparison with normal controls. This fact could be proven by histo-pathological examination. Consequently clinical data, exfoliative cytogy and histo-pathology in case of pericoronitis coincided in their findings.