Recent studies have implied that hydrogen sulfide (H₂S) plays a crucial role in several inflammatory conditions. However, so far little is known about the mechanism by which H₂S provokes the inflammatory response in sepsis. Thus, the aim of this study was to investigate if H₂S regulates sepsis associated systemic inflammation and production of proinflammatory mediators via the activation of NF-B. Male Swiss mice were subjected to cecal ligation and puncture (CLP) induced sepsis and treated with DL-propargylglycine (PAG, 50 mg/kg i.p.), NaHS (10mg/kg, i.p.) or saline. PAG, an inhibitor of H₂S formation, was administered either 1 hour before or 1 hour after CLP while NaHS, a H₂S donor, was given at the time of CLP. Some normal mice were given NaHS (10mg/kg i.p.) to induce lung inflammation with or without pretreatment with the NF-B inhibitor, BAY 11-7082. 8 hours after CLP, both prophylactic and therapeutic administration of PAG significantly reduced the mRNA and protein levels of IL-1, IL-6, TNF- monocyte chemotactic protein-1 (MCP-1) and macrophage inflammatory protein-2 (MIP-2) in lung and liver coupled with decreased activation and translocation of NF-B in lung and liver. Inhibition of H₂S formation also significantly reduced lung permeability and plasma alanine aminotransferase (ALT) activity. In contrast, injection of NaHS significantly aggravated sepsis associated systemic inflammation and increased NF-B activation. In addition, H₂S induced lung inflammation was blocked by BAY11-7082. Therefore, H₂S upregulates the production of proinflammatory mediators and exacerbates the systemic inflammation in sepsis through a mechanism involving NF-B activation.