In surgical stress, internal mediators include cytokines released locally as well as into the circulation; activation of neutrophils, monocytes, macrophages, endothelial cells, platelets and other cells; activation of plasma protein cascade systems such the complement, coagulation, fibrinolytic and contact systems the release of tissue-damaging proteinases; the formation of lipid mediators such as eicosanoids and platelet-activating factor; and the generation of oxygen and nitrogen radicals. In addition, during host defense rections, a number of agents are released that blunt the inflammatory response, such as anti-inflamatory cytokines, soluble cytokine receptors, acute-phase proteins including proteinase inhibitors and stress hormones. In this paper, we explain such internal mediators.