It has been reported that host-derived enzymes, matrix metalloproteinases (MPs), play a major role in periodontal tissue destruction. The purpose of this study was to examine the effects of bacterial supernatant from mixed gram-negative anaerobic bacteria and Porphyromonas gingivalis (P. gingivalis) cultivated from periodontal pockets nad lipopolysaccharide (LPS) of P. gingivalis on expression and activation of MMP-2 in culture of human gingival fibroblasts (HGF) and human periodontal ligament (HPDL) cells. HGF and HPDL were treated with supernatant of mixed gram-negative anaerobic bacteria of supernatant of P. gingivalis for 48 hours. RT-PCR and Western analysis were used to analyze MMP-2 expression at transcriptional and translational level, respectively. The level of MMP-2 activation was monitored by gelatin zymography. It was found that supernatant of mixed gram-negative anaerobes and supernatant of P. gingivalis could indeuce MMP-2 activation, but could not alter the mRNA and protein levels of MMP-2. The MMp-2 activation was inhibited by NF-kB inhibitor and metal chelating agents (EDTA, phenanthroline), but not by serine protease inhibitor (aprotinin, PMSF). These results indicated that HGF/HPDL could directly response to the bacterial supernatant by demonstrating the active form of MMP-2. The next experiment, HGF and HPLD were treated with LPS extracted from P. gingivalis for 48 hours. The results indicated that P. gingivalis LPS could induce MMP-2 activation in both cell types. The mechanism of MMP-2 activation induced by LPS was different from those induced by the supernatant, since the activation process was not inhibited by EDTA or phenanthroline. However, it can be partially inhibited by NF-kB inhibitor and completely blocked by serine protease inhibitor. In addition, LPS induced MMP-2 activation was inhibited by aprotinin and PMSF. These results revealed that the ability of LPS to activate MMP-2 may occur through 2 different pathways, the NF-kB dependent pathway and the serine protease-dependent pathway. In conclusion, bacterial supernatant of mixed gram-negative anaerobes and P. gingivalis, and LPS of P. gingivalis can activate MMP-2 in HGF and HPDL cells by different mechanism. It is possible that secreted bacterial products of gram-negative anaerobes and P. gingivalis play a crucial role in periodontal tissue destruction, by directly activate MMP-2 secreted from HGF and HPDL cells.