It is well established that the resting metabolic rate MR rises dramatically after extensive burn injury, imposing special considerations on the management of burn patients. In order to better understand the efferent limb of the mechanism generating this hypermetabolism, previous investigators have sought to find roles for various endocrine systems andor their related metabolic substrates. These possibilities have included thyroid hormones, catecholamines, carbohydrate and lipid factors as controlled by the endocrine pancreases, glucagon and cortisol. We had the opportunity to follow plasma concentrations of most of these factors longitudinally in a large homogeneous group of patients. In view of these factors longitudinally in a large homogeneous group of patients. In view of the known relationship of MR with total burn size TBS and postburn day PBD, we were able to assess for the first time, and in the same patients, whether the changes in basal plasma endocrine variable are also related to TBS and PBD. Further, we were able to determine whether endogenous variation in the endocrine factors was associated with variation in MR beyond the MR variation explained TBS and PBD.