Recently the presence of carnosine in the kidney has been established, and several potential roles for histamine have been proposed in renal metabolism. Histamine is known to occur in relatively high concentrations in renal tissue of several species and has been implicated in the autoregulation of renal blood flow and glomerular filtration. This study was designed to evaluate the effect ofshock produced by compound 48/80 on the mobilization of renal carnosine to histamine and the effects of various blocking agents such as lodoxamide, diphenhydramine and cimetidine on this mobilization. Our results showed that compound-48/80-induced shock causes significant mobilization of renal carnosine and histidine to histamine and that this response can be blocked by administration of lodoxamide and diphenhydramine, but not cimetidine.