The neuropeptide substance P(SP) has been implicated in the mediation of inflammation and immune-mediated disease such as arthritis. Recently, it was reported that SP was markedly increased around the blood vessels in inflamed gingiva as well as in close association with the inflammatory cell infiltrate. These results support that SP may contribute to the pathophysiology of neuronal inflammation in human periodontal tissues. SP may regulate inflammatory/immune responses by stimulating the proliferation of human T cells, differentiation and antibody-secreting potential of B cells, macrophage respiratory burst, connective tissue proliferation, and the secretion of cytokines from monocytes and T cells. Here, I studied potential role of SP as a costimulatory chemical signal in inflammatory/immune responses, by determining the released proinflammatory cytokines such as $MIP-1{alpha}$, $IL-1{eta}$, and IL-6 from culture supernatants of homogeneous immune cell lines. Serum free cell supernatants were concentrated with TCA precipitation, fractionated with SDS-PAGE, and subjected into western blot analysis. Among 15 cell lines tested, macrophage/monocyte cell line RAW264.7 and WRl9m.1 showed the highest level of induction of $MIP-1{alpha}$ when stimulated with LPS. Discrete IL-6 bands with multiple forms of molecular mass were detected from supernatants of B cell lines A20(32kDa), Daudi(32, 35kDa), and SKW6.4(29kDa), which were expressed constitutively. $IL-1{eta}$ could not be detected by the method of western blot analysis from supernatants of all cell lines tested except RAW264.7, WRl9m.1, and erythroid cell line K562 which showed the least amount of $IL-{eta}$ secretion. SP $10^{-9}M$ with suboptimal dose of LPS treatment showed synergistic induction of $MIP-1{alpha}$ release from RAW264.7 or WR19m.1, and also IL-6 release from A20, but this synergism is not the case in costimulation of RAW264.7 or WRl9m.1 with SP $10^{-9}M$ and TPA. Although treatment of T cell line CTLL-R8 with SP $10^{-7}M$ or PHA+TPA induced modest level of $MIP-1{alpha}$ secretion, synergism was not observed when they are applied together. These findings all together suggest the possibility of a regulatory role of SP in inflammatory/immune reaction through differential modulation of bioactivities of other chemical cosignals.