The release of histamine and mortality was studied in mice after various types of experimental shock. In burn shock, serum histamine rose significantly after injury, but there was no correlation between increased serum histamine and high mortality as a consequence of several therapy regimes. For example, after treatment with histamine or Compound 48/80 before burning, there was a rise of serum histamine, yet shock mortality fell significantly. Although separate administration of antagonists of H 1 - or H 2-histamine receptors had no effect on mortality, pretreatment with both diphenhydramine and burimamide significantly increased shock mortality. In tourniquet shock, serum histamine rose significantly, and treatment with both antagonists before trauma produced a significant elevation of shock mortality. In endotoxin shock, prior treatment with one or both drugs did not change mortality. These results suggest that endogenous histamine is not a lethal factor in burn and tourniquet trauma, but rather it appears to have a compensatory, beneficial effect.