It is recognized that extensively burned patients have an increased susceptibility to infection and often succumb to multiple organ failure related to sepsis. Numerous investigations performed over more than 30 years have demonstrated immunologic abnormalities in burn patients, including changes in serum immunoglobulin and opsonin levels, alterations in the complement system, impairment of phagocyte and neutrophil function, suppression of delayed hypersensitive reactions, and prolongation of allograft survival. Recent progress in immunology has shown that inadequate production of both cytokines and arachidonic acid derivatives is profoundly involved in immunosuppression after severe burn injury. A better understanding of immunologic status is necessary to reduce the mortality rate from infection in extensively burned patients. This may also lead to discovering the therapeutic control mechanisms for their immunity.