Burn infection occurs when pathogenic bacteria colonized on the burn wound surface, and they then invaded the viable tissue causing sepsis or sepsis with blood stream invasion. This infection pattern is particular to burn injury. Both in a model of pseudomonas burn wound sepsis and a clinical study of early eschar excision for bacteria quantification indicate that the bacteria not only are located on the burn wound surface but also invaded the deeper tissues. Finally, the bacteria penetrate into the neighboring viable tissue and even blood vessels. Therefore, we can say that burn infection is from local wound infection to invasive infection, and finally sepsis is developed ,and it is termed as burn wound sepsis. The cutoff count of subeschar tissue bacteria is 10(5)/g. However, the burn wound sepsis may not occur when the number of subeschar tissue bacteria reaches 10(5)/g. The criteria for the diagnosis of burn wound sepsis are mainly listed as below: (1) The number of bacteria in the subeschar reaches > or =10(5)/g. (2) Bacteria can be detected in the biopsy specimen. (3) Sepsis associated symptoms and signs. However, the sepsis associated symptoms and signs must be obvious in patients to make the clinical diagnosis of burn wound sepsis. If the sepsis associated symptoms and signs do not appear, we should not make the diagnosis of burn wound sepsis eyen with the number of bacteria in the subeschar tissue reaching 10(5)/g or bacteria can be found in the biopsy specimen. Sepsis has been defined as the body % response to bacteria and their products. The occurrence of sepsis depends primarily on immune function and stress response intensity, and it is closely related to wound infection degree such as bacteria density and invasion depth in the burn wound, or plasma endotoxin level to certain extent.