To collect information which would aid in our understanding of normal immune responses to microbes of the body flora, lymphocyte transformation studies were done on a representative sampling of the general population. The sampling included people with varying degrees of periodontal disease who were otherwise medically healthy. The objectives of this study were to assay lymphocyte transformation responses to several plaque and non-plaque bacterial antigens, to begin to establish the range and normal limits of lymphocyte responses to these antigens within a group of people felt to be representative of the general population, and to attempt to more clearly define the role of the immune response in general and lymphocyte transformation in particular in the pathogenesis of periodontal disease.