Prevotella intermedia, a major periodontal pathogen, plays important roles in the initiation and development of periodontitis by stimulating the release of proinflammatory cytokines, proteinases and matrix metalloproteinases (MMPs). Our previous study demonstrated that P. intermedia induced MMP-9 expression in human periodontal ligament (hPDL) cells. In this study, we examined the effects of P. intermedia on other MMPs' expression. Semi-quantitative reverse transcriptase (RT)-PCR analysis revealed that P. intermedia ATCC 25611 supernatant increased MMP-1 and MMP-8 mRNA expression in a concentration- and time-dependent manner. Enzyme-linked immunosorbent assay and Western blot results confirmed the RT-PCR results at the protein level. Cyclooxygenase inhibitor indomethacin significantly attenuated the upregulatory effects of P. intermedia on MMP-1 and MMP-8 expression. Extracellular signal-related kinase inhibitor PD98059 and c-Jun N-terminal kinase inhibitor SP600125 considerably decreased the upregulated level of MMP-1, whereas p38 inhibitor SB203580 markedly inhibited MMP-8 expression, suggesting that prostaglandin E(2) and mitogen-activated protein kinase signaling pathways are involved in P. intermedia-induced MMP-1 and MMP-8 upregulation. Our results indicate that P. intermedia might contribute to periodontal connective tissue and bone matrix destruction through upregulating MMP production.