The lipopolysaccharide endotoxin macromolecules are cell wall's components of the Gram negative bacteria. The endotoxins are produced by Gram negative bacteria of intestinal flora. If the endotoxins are translocated from the intestinal tract to the circulation or injected into bloodstream, they elicit (depending from the quantity of endotoxin), slight or serious effects (e.g. endotoxin shock). In the effects of endotoxin certain cell populations (e.g. thrombocytes, macrophages, leukocytes, etc.), certain organs and organ-systems (e.g. liver, spleen, bone marrow, endocrine and lymphoreticular systems etc.) are involved. Effects of endotoxin are produced by mediators (e.g. endotoxin binding proteins, cytokines, prostaglandins, prostacyclins, NO etc.). The endotoxin sensitivity of vertebrate organisms is dependent from the phylogenetical status of the species. Most sensitive species is the human. Generally accepted that endotoxin has an important role in the pathogenesis of septic shock. In other pathological processes (e.g. intestinal syndrome of radiation disease, Gram negative infections, various shock forms etc.) are supposed or proved the role of endotoxins. Lead acetate induced endotoxin hypersensitivity or LAL methods are good tools for demonstration of the role of endotoxin in the pathogenesis of various processes. For this reason, the experimental endotoxin shock is used a model of septic and other shocks.