This study investigated whether an improvement in periodontal health resulted in changes in the prevalence of periodontopathogenic bacteria in saliva and tongue coatings and a reduction in volatile sulfur compounds (VSCs: H(2)S and CH(3)SH) linked to oral malodour. The subjects were 35 patients who visited the breath odour clinic of Kyushu Dental College, Japan. Their mean age was 51.2+/-18.3 years (mean+/-sd). A clinical examination performed at baseline and 2 months after periodontal treatment assessed VSCs in mouth air using gas chromatography, periodontal probing depth and bleeding on probing (BOP) in all subjects; saliva and tongue coatings were also collected. Genomic DNA was isolated from the samples, and the proportions of five periodontopathogenic bacteria (Porphyromonas gingivalis, Tannerella forsythensis, Treponema denticola, Prevotella intermedia and Prevotella nigrescens) were investigated using quantitative real-time PCR. The subjects were classified into four groups based on the presence of a periodontal pocket of more than 4 mm (PD) and VSCs above the organoleptic threshold level (VSCT) as follows: -PD/-VSCT group, subjects without PD or VSCT; -PD/+VSCT group, those without PD but with VSCT; +PD/-VSCT group, those with PD but without VSCT; and +PD/+VSCT group, those with PD and VSCT. Although the mean PD values in the +PD/-VSCT and +PD/+VSCT groups, BOP in the +PD/+VSCT group, and H(2)S and CH(3)SH concentrations in the -PD/+VSCT and +PD/+VSCT groups were greater than in the other groups at baseline, we found no significant difference among the four groups after periodontal treatment. The proportion of periodontopathogenic bacteria in saliva was higher in the +PD/-VSCT and +PD/+VSCT groups than in the -PD/-VSCT and -PD/+VSCT groups at baseline and after treatment, but the proportions of bacteria in saliva after treatment were reduced compared to the baseline. Furthermore, the differences in the proportions of the five target bacteria in the tongue coating were not as apparent as those in saliva at baseline or after treatment. The prevalence of periodontopathogenic bacteria in saliva may reflect periodontal health status and influence VSC levels in mouth air.