Poly (ADP-ribose) polymerase-1 is a nuclear DNA-binding protein that participates in the DNA base excision repair pathway in response to genotoxic stress in mammalian cells. Here we show that PARP-1-deficient cells are defective in NF-κB-dependent transcription activation, but not in its nuclear translocation, in response to TNF-α. Treating mice with lipopolysaccharide (LPS) resulted in the rapid activation of NF-κB in macrophages from PARP-1+/+ but not from PARP-1−/− mice. PARP-1-deficient mice were extremely resistant to LPS-induced endotoxic shock. The molecular basis for this resistance relies on an almost complete abrogation of NF-κB-dependent accumulation of TNF-α in the serum and a down-regulation of inducible nitric oxide synthase (iNOS), leading to decreased NO synthesis, which is the main source of free radical generation during inflammation. These results demonstrate a functional association in vivo between PARP-1 and NF-κB, with consequences for the transcriptional activation of NF-κB and a systemic inflammatory process.