Hepatic ischemia occurs in the settings of trauma, transplantation, and elective liver resections. The initiating events that account for local organ damage are only partially understood. Interferon regulatory factor-1 (IRF-1) is a transcription factor that regulates the expression of a number of genes involved in both innate and acquired immunity; however its function in liver injury is unknown. Therefore, the purpose of this study was to investigate the role of IRF-1 in hepatic ischemia-reperfusion (I/R) injury. In C57BL/6 mice undergoing 60 minutes of hepatic ischemia, IRF-1 protein expression increased as early as one hour after reperfusion. IRF-1 knockout mice were significantly protected from hepatic I/R-induced damage compared to their wildtype controls. Hepatic I/R injury resulted in marked activation of the MAP kinase JNK in the wildtype, but not IRF-1 knockout mice. The IRF-1 knockout mice also exhibited significantly lower hepatic expression of TNF, IL-6, ICAM-1, and inducible nitric oxide synthase (iNOS) mRNA. Adenoviral delivery of IRF-1 into C7BL/6 mice resulted in increased liver damage even without an ischemic insult. This injury was associated with increased JNK activation and hepatic inducible nitric oxide synthase (iNOS) expression. Since IRF-1 contributed to liver injury, we also examined for inflammatory signals that regulated IRF-1 gene expression in cultured hepatocytes. IFN and IFN were strong inducers of IRF-1 mRNA (>10-fold) in a time- and dose-dependent manner, while TNF and IL-1 also induced IRF-1 mRNA to a lesser extent (2-3 fold). IL-6 and lipopolysaccharide had no effect on IRF-1 expression. This study demonstrates that IRF-1 exerts a harmful role in hepatic I/R injury by modulating the expression of multiple inflammatory mediators. We further show that IRF-1 mediated injury involves the activation of JNK, and that hepatocellular IRF-1 expression itself is regulated by specific cytokines.