Previous studies reported both beneficial and detrimental roles of hydrogen sulfide (H2S) in various models of critical illness. The goal of our study was to compare the outcome of septic shock in wild-type mice and in mice deficient in cystathionine-gamma-lyase (CSE). Mice were subjected to sepsis by cecal ligation and puncture and survival was monitored for 48 h. In a separate study, animals were sacrificed at 24 h post-CLP, vascular function was evaluated ex vivo and indices of organ function were measured. At 30 h, there was 20% mortality in CSE−/− mice, while no mortality in the wild-type controls. By 36 h, the mortality increased to 50% in CSE−/− mice, while it remained low (10%) in the wild-type controls. However, by 46 h, the two survival curves converged, and showed a similar, 60% mortality in both groups. Analysis of the plasma markers of organ injury revealed slight trends for a CLP-induced increase in the liver injury markers ALT and AST and the pancreatic injury marker amylase in wild-type mice. More pronounced increases were noted in the same parameters in the CSE−/− mice. Blood urea nitrogen levels were elevated 3-fold over baseline in wild-type mice subjected to CLP and 4-fold over baseline in CSE−/− mice. There was an impairment of endothelium-dependent relaxation responses in the thoracic aorta after CLP, which was more pronounced in the CSE−/− mice. These data indicate that CSE, and its product, H2S, exerts protective effects against the development of sepsis, especially in the early stages of the disease.