Endotoxin and exotoxin are both bacterial toxins, generally speaking, those released outside the bacterium are called bacteriophage exotoxins, while those present in the bacterium and released after destruction of the bacterium are called bacteriophage endotoxins. The difference between the two is mainly in terms of source, chemical composition, stability, toxic effects and immunogenicity, etc. 1, source: endotoxin mainly from Gram-negative bacteria, and exotoxin often from Gram-positive bacteria, but some Gram-negative bacteria such as tetanus, diphtheria rod-shaped bacteria can also produce exotoxin; 2, chemical composition: the main component of endotoxin is phospholipid-polysaccharide-protein complex, while the main component of exotoxin is protein. And the main component of exotoxin is protein; 3, stability: the nature of endotoxin is more stable, heat resistance is higher, in the environment of 60 ℃ can be tolerated for several hours. While the stability of exotoxin is poor, at 60 ℃ can be rapidly destroyed; 4, toxic effects: compared to the toxic effects of endotoxin is slightly weaker, and the toxic effects of various bacterial endotoxin is roughly the same. Often cause fever, disseminated intravascular coagulation, granulocytopenia and Schwarzman’s phenomenon; exotoxins have stronger toxic effects, and various exotoxins are selective, can cause host-specific lesions and not easy to cause fever. Can inhibit protein synthesis, and has cytotoxicity, neurotoxicity, etc.; 5, immunogenicity: endotoxin can only stimulate the body to produce antibodies to polysaccharide components, can not form antitoxin, so it can not be processed as a toxoid; and exotoxin is stronger, can stimulate the body to produce highly effective antitoxin, can be used for artificial automatic immunity.