The mechanism by which LPS or phorbol 12-myristate 13-acetate (PMA) induces production ofproinflammatory cytokines in murine macrophages, and a role for phosphatidylinositol 3-kinase(PI3-kinase) had not been well investigated. Activation of the transcription factor, nuclear factors-kB (NF-kB), is initiated by the phosphrylation of the inhibitory subunit, IkB, which targets IkB fordegradation and leads to the release of active NF-kB. In this study we demonstrate that 2-(4-morpholinyl)-8-phenylchromone (LY294002) which inhibits PI3-kinase specifically inhibiteddegradation of IkBa in the RAW264.7 cells stimulated with IFN-g plus LPS or IFN-g plus PMA. Toelucidate the importance of this activity in RAW 264.7 cells, we examined TNF-a and IL-6production in the activated cells. Pretreatment of the cells with LY294002 results in the inhibitionof TNF-a and IL-6 production in the RAW264.7 cells stimulated with IFN-g plus LPS or IFN-g plusPMA. Furthermore, LY294002 inhibited the production of nitric oxide (NO) in the RAW264.7 cellsstimulated IFN-g plus LPS or IFN-g plus PMA. LY294002 also potentially inhibited inducible NOsynthase (iNOS) mRNA expression in the activated RAW264.7 cells. In conclusion, the presentresults suggest that PI3-kinase is involved in the signal transduction pathway responsible forLPS- or PMA-mediated TNF-a and IL-6 production, and that LY294002 inhibits NO generationthrough blocking the degradation of IkBa in the activated RAW264.7 cells.