Corticosteroids were originally considered for use in sepsis more than 30 y ago. Substantial preclinical data supported their potential benefit. However, in initial clinical studies these agents used in very high doses were not beneficial and in some cases may have been harmful. Subsequent clinical studies however, have suggested that much lower doses (i.e. physiologic stress dose steroids) may be beneficial. A metaanalysis of both earlier and more recent studies support continued investigation of physiologic dose corticosteroids in sepsis. The mechanism of action is likely multi-fold, including the correction of relative adrenal insufficiency, enhancement of the action of endogenous catecholamine and the inhibition of inflammation via interactions with inflammatory gene expression. Use of heparin in sepsis has also shown early benefit in animal models. Furthermore, review of three recent large phase III trials in sepsis, has shown control patients receiving low dose heparin to have consistently better outcome than control patients who did not receive heparin. Although there are several possible reasons for these effects, one is that low dose heparin may itself be protective in sepsis. Another recent large clinical trial comparing the effects of low molecular weight heparin to placebo in critically ill patients, some of whom presumably presented with sepsis, also showed improved outcome with this type of treatment. The effects of heparin may be two fold at the least. On the one hand, the anticoagulant effects may be directly beneficial by limiting intravascular thrombin production, inhibit the process of DIC and the end organ injury that would result from an interrupted blood supply. However, thrombin production in sepsis may itself precipitate inflammatory mediator release, suggesting that anti-thrombin agents such as heparin may also have anti-inflammatory effects. Thus, corticosteroids and heparin, while having some actions that are independent, may have others, specifically anti-inflammatory ones, that are overlapping. Both physiologic dose corticosteroids and low dose heparin are increasingly used together in patients with sepsis. Understanding whether their effects interact is important for understanding how best to apply these agents clinically. Furthermore, the combination of these two relatively inexpensive agents with well known side effects may be much more effective than the application of newly developed agents for sepsis such as activated protein C which is proposed to have anticoagulant and anti-inflammatory effects. The present experiment is designed to investigate the effects of corticosteroids and heparin alone and in combination in a mouse model of E. coli pneumonia and sepsis. In the first part, doses of corticosteroid or heparin alone will be determined that result in improved survival rates. Literature review has suggested that in antibiotic treated mouse models similar to ours, the effective dose range of hydrocortisone and heparin will be 5 to 125 mg/kg and 100 to 2500U/kg respectively. Therefore we will study hydrocortisone in doses of 0, 5, 25 or 125 mg/kg and heparin in doses of 0, 100, 500 or 2500 U/kg. Once the doses of these individual agents have been determined which increase survival, their effects alone or together both on survival and on measures of microbial clearance, cytokine production, both intravascular and extravascular leukocyte responses, coagulation studies, and changes in tissue histology will be compared.