Septic shock (SS) is the most common type of shock encountered by internists, and its prevalence appears to be increasing. SS complicates all types of infections. The hemodynamic characteristics of SS include a low systemic vascular resistance and an elevated, but relatively inadequate, cardiac output. A cardiomyopathy frequently occurs. The major endogenous mediator of SS is tumor necrosis factor, and interleukins-1 and -2 may also contribute. Important secondary phenomena include release of platelet activating factor, vasodilator prostaglandins, and upregulation of adhesion molecules on polymorphonuclear leukocytes and endothelial cells. Current therapy is often ineffectual, and potentially promising new therapeutic approaches are reviewed.