The activation of monocytes and macrophages induced by lipopolysaccharide has been shown to contribute to the binding of lipopolysaccharide and lipopolysaccharide-binding protein complex to the cell surface CD14 molecule. To clarify the mechanism of the lipopolysaccharide-induced modulation of the function of gingival fibroblasts, we investigated the effect of anti-CD14 on interleukin 6 (IL-6) production on human gingival fibroblasts in vitro. Immunochemical staining revealed weak positivity for CD14 on fibroblasts from healthy gingiva, while strong positivity for CD14 was found on fibroblasts from inflamed gingiva. Western blot profiles of the fibroblasts and monocytes showed a CD14-positive reaction at 55 kDa. Fluorescein isothiocyanate-conjugated Escherichia coli lipopolysaccharide bound to fibroblasts more strongly in the presence of 10% fetal bovine serum than without serum. This binding, as well as IL-6 production, was blocked by anti-CD14 monoclonal antibody. The results showed that CD14 was present on human gingival fibroblasts, which suggests that lipopolysaccharide modulation of gingival fibroblast function depends on CD14.