Within the in vivo environment human gingival fibroblasts (HGF) are challenged with bacteria or their products resulting in the release of inflammatory mediators and cell--signaling macromolecules. These mediators and cytokines manifest potent immune regulatory and catabolic activity and may play key roles in periodontal disease processes. The purpose of this study is to examine the ability of formalin-killed whole bacterial cells of Actinobacillus actinomycetemcomitans and Campylobacter rectus to alter the production of prostaglandin E2 (PGE2), and interleukins 1beta (IL-1beta), 6 (IL-6) and 8 (IL-8) by HGF in vitro. Characterization of cytokine and inflammatory mediator production by HGF will be directed at 3 cell functional levels: secretion, protein synthesis and gene transcrption. Secretion of PGE2, IL-1beta, IL-6 and IL-8 by HGF following bacterial challenge was quantified by analyzing culture supernatants using radoimmuno assays. Bacterial interspecies and intraspecies variations , as well as the effect of human serum antibodies on mediator and cytokine secretion have been examined. The secretory responses of HGF from normal, adult periodontitis and localized juvenile periodontitis subjects have been compared. Future research efforts will be directed towards the quantitation and intracytoplasmic localization of cytokine and mediator protein and mRNA synthesis using immunocytochemical and molecular methodologies.