Lymphocyte membrane-associated IgG subclass antibodies in human periodontal disease were studied to ascertain the relative presence of cytophilic IgG antibodies and the membrane Fc receptors which bind them. The experimental approach correlated the effect of incubating gingiva in tissue culture medium to remove cytophilic antibodies with the changes in the number of Fc receptors detectable after washing. The evidence indicated that the majority of lymphocytes in mild gingivitis lesions lacked cytophilic IgG antibodies as well as Fc recetors. In severe gingivitis, the number of IgG subclass bearing lymphocytes increased to about half of the total lymphoid population, while the percentage of Fc receptor bearing cells remained quite low (12.3 % +/- 3.2, S.E.). The majority of IgG subclass bearing lymphocytes had membrane IgG which serve as receptors for antigen; such cells are classically defined as bone marrow (B) derived lymphocytes and serve as the progenitor for plasma cells. Gingival specimens for patients with periodontitis were found to contain the highest percentage of Fc receptor bearing lymphocytes (38.3% +/- 12.6 S.E.) and cytophilic IgG antibodies. The findings indicate that the clinical stages of human periodontal disease are characterized by different populations of infiltrating lymphocytes.