The purpose of this investigation was to find out the relationship between volatile sulphur compounds in incubated whole saliva and that in mouth air, and between the former and cellular elements in whole saliva in periodontal patients.The subjects were divided into the following three groups based on clinical findings and intensity of odour measured by olfactory panel of trained judges; the periodontal patients with halitosis (P-H group), the periodontal patients without halitosis (P-N group) and the normal subjects (N group)The test samples used this investigation were unstimulated whole saliva and that were incubated at 37°C.The amount of valatile sulphur compounds produced from incubated whole saliva and that in mouth air were measured by gas chromatograph equipped with flame photometric detector, while the number of leucocytes and epithelial cells in whole saliva were counted by Klinkhamer's technique.The degradation of leucocytes and epithelial cells in incubated whole saliva were observed using smear speciments staind with hematoxylin and eosin.Results were as follows1. The average number of leucocytes in whole saliva were 11764/cmm in P-H group, 3085/cmm in P-N group and 434/cmm in N group. Obvious differences were observed among three groups. The average number of epithelial cells in whole saliva were 1381/cmm in P-H group, 1157/cmm in P-N group and 310/cmm in N group. There were no differences between P-H group and P-N group.2. The methyl mercaptan produced from incubated whole saliva in P-H group was detected earlier in time and largier in quantity than other two groups.3. In P-H group, obvious correlation was observed between number of leucocytes in whole saliva and methyl mercaptan contents in mouth air, however, no correlation was observed between number of epithelial cells in whole saliva and methyl mercaptan contents in mouth air. In all subjects, obvious correlation was observed between number of leucocytes and the highest value of methyl mercaptan contents produced incubated whole saliva, however, no correlation was observed between number of epithelial cells and the highest value of methyl mercaptan contents produced incubated whole saliva.4. Number of leucocytes in whole saliva were observed high correlation with gingival score, bleeding, discharge of pus and pocket depth, but no correlation between plaque score.5. Leucocytes in incubated whole saliva degraded rapid and they were almostly not observed in 4 hours after incubation, however, degradation of epithelial cells were observed about 8 hours after incubation.