Porphyromonas gingivalisplays a major role in the pathogenesis of periodontal disease, however some individuals withP. gingivalisinfection do not experience periodontal breakdown. The aim of this study was to investigate the proliferative responses of two highly defined groups of subjects and to establish and characterize peripheral blood and gingival cell T cell lines and clones from subjects from these groups, The two groups were selected on the basis ofP. gingivalisin their plaque and the presence of serum anti‐P. gingiralisantibodies. Both groups therefore were seen to haveP. gingivalisand to have responded to it. They however differed only in their clinical susceptibility (adult periodontitis) or resistance (gingivitis) to periodontal breakdown. Dose responses of peripheral blood mononuclear cells extracted from the subjects showed a trend towards a lower response by the adult periodontitis group toP. gingivalisouter membrane (OM) antigens. Peripheral blood T cell lines and clones responsive toP. gingivalisOM were established from a high responding gingivitis subject and a low responding adult periodontitis subject. Gingival T cell lines and clones were also derived from cells extracted from the periodontal tissues of the same periodontitis subject. The majority of T cells in the peripheral blood T cell line from the gingivitis subject were CD4 while those from the adult periodontitis subject were CD8. The gingival T cell line was CD3+ve CD4‐ve and CD8‐ve. All lines and clones proliferated slowly toP. gingivalisOM but phytohaemagglutinin (PHA) induced an increase in DNA synthesis in those derived from the gingivitis subject with little to no effect on those established from the adult periodontitis subject. Furthermore. PHA inhibited the proliferative response of the CD8 clone derived from the adult periodontitis subject. Phenotypic analysis demonstrated that all the peripheral blood clones expressed the αβ TCR while the gingival T cell clones expressed the γδ TCR. All clones had the memory/primed CD45RO+ve phenotype and at least 80% of cells in each clone were HLA‐DR + ve. A lower percent of gingival cells expressed CD45RA than the CD4 peripheral blood clones and the two CD8 clones also had a decreased CD45RA expression. The gingival T cell clones also expressed a low percent CD25 as did the CD8 clone derived from the adult periodontitis subject. The results suggest that clones derived from the gingivitis and adult periodontitis subject may be functionally different. The presence of γδ T cells in adult periodontitis remains to be confirmed and their functi