Clinical manifestations of sepsis, such as systemic inflammatory response and multiple organ dysfunction syndrome, are considered to be the results of a decompensated host defense response. If tissue injury is sufficiently severe to overwhelm local defense mechanisms, systemic activation of these essentially protective mechanisms may lead to autodestructive "host defense failure disease." This is not always caused by invading bacteria; sterile inflammation such as results from multiple trauma or pancreatitis can initiate a similar response. Evidence suggests that the activation of the macrophage/monocyte system that underlies the systemic inflammatory response may reflect one facet of a more generalized dysregulation of intercellular communication, as well as a dysfunction of such subcellular processes as signal transduction or stress gene expression. Alterations in signal transduction or stress gene expression can affect the host defense response to subsequent stressful events in either a negative or a positive sense. In particular, the sequential induction of acute phase and heat shock response may initiate programmed cell death, reflecting a potential molecular mechanism for the development of multiple organ dysfunction syndrome. The development of anti-inflammatory treatment strategies seems to be hampered by the discrepancy between locally protective and systemically detrimental properties of the host defense response.