P. gingivalis has been implicated as a strong pathogen in periodontal disease and known to have three serotypes of P. gingivalis. The purpose of this study is to investigate on the relationship between virulence, metabolic acids and genetic heterogeneity of P. gingivalis. P. gingivalis W50 standard strain and five strains of P. gingivalis serotype b Korean isolates were used in this study. For in vitro virulence test, lyophilized whole cell P. gingivalis were suspended, and sonicated with ultrasonic dismembranometer. Sonicated samples were applied to cultured cells derived from periodontal ligament, and cell activity was assayed with growth and survival assay. The metabolic acids were also extracted, and determined by High Performance Liquid Chromatography. Pst I-digested bacterial genomic DNA was electrophoresed, and densitometric analysis was performed to study the genetic heterogeneity. All of the P. gingivalis serotype b produced butyric acid. In cell activity study, butyric acid inhibited the cell activity irrespective of its concentration. Densitometric analysis showed restriction fragment length polymorphism. These results suggested that there existed heterogeneity of the metabolic acids and the virulence of P. gingivalis and such heterogeneity might be related to genetic heterogeneity.