Although it has been well known that the role of LPS on liver damage is mediated through TNF-alpha, the direct cytotoxic effect of LPS on IFN-gamma-primed hepatocytes has not yet been clearly demonstrated. Here, we demonstrate that the IFN-gamma-mediated death of murine embryonic liver BNL- CL2 cells is potentiated by treatment of LPS (0.5 ug/ml). In addition, over 25 uM of sodium nitroprusside (SNP), an exogenous NO donor, significantly prevents cell death by IFN-gamma alone or IFN-gamma plus LPS (IFN-gamma/LPS) in a dose-dependent manner. In addition, SNP efficiently blocked death of BNL-CL2 cells only when it was added within 12 hr after treatment of IFN-gamma and IFN-gamma/LPS. However, potassium ferrocyanide (PFC), a structural analog of SNP, did not show any protective effect on the IFN-gamma alone or IFN-gamma/LPS-induced BNL-CL2 cell death. The preventive effect of SNP occurs in parallel with the suppression of caspase 3-like protease activation. In addition, we have demonstrated that a relatively high concentration as well as an appropriate period of exposure to NO may be critical to maintain cell viability against cytotoxicity by IFN-gamma and IFN-gamma LPS. Furthermore, the preventive effect of SNP in IFN-gamma/LPS-induced cell death is mediated by a protein kinase G (PKG)-independent manner.