Gingival mononuclear cell production of interleukin 1 (IL-1), interleukin 6 (IL-6) and transforming growth factor-beta (TGF-beta) after stimulation with the putative periodontopathic bacteria, Porphyromonas gingivalis and Fusobacterium nucleatum was investigated. Using an ELISA method, gingival mononuclear cells extracted from 18 adult periodontitis subjects were found to be producing IL-1. However, IL-1 activity could only be detected in 5 out of these 18 cases when tested using a thymocyte proliferation bio-assay, suggesting the presence of IL-1 inhibitors. Depletion of monocytes from peripheral blood cultures resulted in a significant decrease in IL-1 activity following P. gingivalis stimulation while there was no effect in the level of IL-1 activity following stimulation with F. nucleatum. This suggests that P. gingivalis and F. nucleatum stimulate different cell types to produce IL-1. Like IL-1, IL-6 production by gingival mononuclear cells was significantly greater than that produced by the control peripheral blood mononuclear cells. Following P. gingivalis and F. nucleatum stimulation, higher levels of IL-6 could be detected; however, both organisms stimulated similar levels. Intracytoplasmic immunofluorescence staining demonstrated a lower percent TGF-beta+ cells in bacterial stimulated peripheral blood mononuclear cell cultures compared with cells in medium alone. In the gingival mononuclear cell cultures, the percentage TGF-beta+ cells peaked at day 1 in F. nucleatum-stimulated, whereas in P. gingivalis-stimulated cultures the peak TGF-beta+ cells occurred at day 3, again suggesting stimulation of different cell subsets. These results illustrate that different periodontopathic bacteria may stimulate different cell types to produce cytokines which may have synergistic or antagonistic effects.