The purpose of this study was to examine the effects of surface-associated material (SAM) from Porphyromonas gingivalis, a major cause of inflammatory periodontal disease, on the production of nitric oxide (NO) and expression of inducible nitric oxide synthase (iNOS) in the murine macrophage cell line RAW264.7. We also attempted to throw light on the signaling mechanisms involved in P. gingivalis SAM-induced NO production. SAM from P. gingivalis 381 was obtained by saline extraction. NO production was assayed by measuring the accumulation of nitrite in culture supernatants. Western blot analysis of iNOS and analysis of reverse transcription-polymerase chain reaction (RT-PCR) products were carried out. We found that P. gingivalis SAM can induce iNOS expression and stimulate the release of NO without additional stimuli and demonstrated an important role of the transcription factor NF-kappaB and microtubule polymerization in NO production. The production of NO required L-arginine, protein tyrosine kinase, and protein kinase C. The ability of P. gingivalis SAM to promote the production of NO may be important in the pathogenesis of inflammatory periodontal disease.