Human gingival tissue biopsies were classified as “initial or early” or “established or advanced” periodontal lesions on the basis of the histopathological criteria of Page and Schroeder (1976). The percentage of plasma cells in each specimen that could recognize somatic antigens associated with one of four bacterial strains was then determined by incubating frozen sections of the gingiva with rhodamine‐labeled bacterial cells. The sections were also briefly incubated with a fluorescein‐labeled antibody to human immunoglobulins to facilitate plasma cell detection. Of the bacterial strains tested (Bacteriodes gingivslis, Actinomyces viscosusstrains ATCC 27044 and T14–V, andActinobacillus actinomycetemcomitans). onlyB. gingivaliswas found to bind to a significantly higher percentage of plasma cells in the more advanced lesions as compared with the earlier lesions (16.3 % versus 3.7 %). These results suggest an important role for somatic antigens associated withB. gingivalisin the immunopathogenesis of human