Using two procedures known to enhance shock-induced defensive fighting (SIF) and mouse-killing--septal lesions and 5,7-DHT lesions--we determined if a 5% tryptophan-loaded diet could reverse the lesion effects. The results indicated that SIF, but not mouse-killing, could be maintained at normal levels following dietary tryptophan loading in both septally lesioned and 5,7-DHT lesioned rats. This behavioral reversal was independent of pain sensitivity, feeding, drinking and body weight levels. Regional brain analysis of monoamines and metabolites indicated that the lesions produced substantial depletions in 5-HT and 5-HIAA with minimal reduction or no change in catecholamines. Dietary tryptophan loading elevated 5-HT and 5-HIAA in unlesioned animals and partially restored 5-HT and 5-HIAA levels in lesioned animals. These patterns of depletion and repletion were confined to the hippocampus following septal lesions and distributed throughout the brain following 5,7-DHT lesions. The results are discussed in terms of a possible hippocampal mediation of the dietary tryptophan reversal in shock-induced defensive fighting following lesioning.