The purpose of the present study was to investigate the involvement of cyclooxygenase-1(COX-1) and cyclooxygenase-2 (COX-2) in PGE2 production by human gingival fibroblasts stimulated with lipopolysaccharides (LPS) from periodondopathogenic bacteria. LPS were isolated from Porphyromonas gingivalis (P. gingivalis), Actinobacillus actinomycetemcomitans (A. actinomycetemcomitans) and Eschericia coli (E coli) by the phenol-water procedure. The three LPS preparations produced PCE2 up to 48 h in a time-dependent manner in human gingival fibroblasts. P. gingivalis-LPS was the most potent stimulator of PGE2 production and, to a lesser extent, A actinomycetemcomitans- and E coli-LPS. Treatment of the cells with indomethacin, a non selective COX-1/COX-2 inhibitor and NS-398, a selective COX-2 inhibitor, completely depressed PGE2 production. Treatment of dexamethasone, known to inhibit COX-2 expression, also significantly prevented PGE2 production. Immunohistochemical staining of COX-2 protein demonstrated that expression of COX-2 protein was increased at 24 h after P gingivalis-LPS stimulation, while expression of COX-1 protein was not affected by P. gingivalis-LPS. In order to investigate the regulation of PGE2 production. P. gingivalis-LPS-stimulated cells were treated with herbimycin A and genistein, both inhibitors of tyrosine kinases. Both the inhibitors significantly inhibited PGE2 production. Herbimycin A treatment depressed expression of COX-2 protein. These data suggest that human gingival fibroblasts stimulated with LPS from periodontopathogenic bacteria mainly produce PGE2 not by COX-1, but by COX-2, induction of which may be regulated by tyrosine kinase and that the produced PGE2 may be involved in the pathogenesis of periodontal diseases.