A number of work on the saliva has been made by many authors, but chemical investigations particuarly on histamine of the saliva are few. Only those by Feldberg, Kamenowa, Sanders and Ungar et al. could be found. However, there has been no study on the histamine content of saliva at the onset of diseases in the oral cavity and its fluctuation at various kinds of surgery. Now quantiative determination was made on histamine content of the saliva in normal and pathological conditions of the oral cavity, and the relationship between the histamine content and the findings of exfoliative cytology was also investigated. One hundred and forty-five patients were examined: 46 of normal healthy control, 26 of acute inflammation, 37 of chronic inflammation, 6 of chronic non-inflammatory lesion, and 30 of minor surgery. Parotid saliva collected by Umemoto-Kakudo's Aspirator and mixed resting saliva were used as test materials. Assay of histamine was made by biological determination by means of Magnus' Apparatus after extraction of histamine by Code's Methode and then Mayeda's Method by neoantsrgan was adopted. In normal healthy controlshistamine contents of the parotid saliva and the mixed saliva were 0.015±0.002 μg/c.c. and 0.034±0.003 μg/c.c. respectively, which were almost equal to those in cases of slight degree of caries or edentulous jaws. In acute inflammation they were 0.036±0.002 μg/c.c. and 0.122±0.016 μg/c.c.. Histamine in the mixed saliva was markedly increased. In chronic inflammation they were 0.026±0.003 μg/c.c. and 0.119±0.019 μg/c.c.. Histaminee in the mixed saliva was increased especially in superficial and extensive lesions. In chronic non-inflammatory lesions they ware 0.018±0.004 μg/c.c., and 0.040±0.013 μg/c.c.. An increase of exfoliated epithelial cells, lescocytes, especially neutrophils, and bacilli were observed in acute inflammatory leasians with particulary high histamine content in the saliva. At the time of various procedures of oral surgery almost no change was observed in the parotid. saliva, while higher histamine content was noticed in the mixed saliva in major surgery than in minor one. Some considerations and discussions were made on the problems of histamine release and on the use of antihistamine preparations from the results obtained and the review of previous litrature.