In a foot shock-induced fighting (FSIF) test, serotonergic and antiserotonergic agents were examined. Stimulation of the brain 5-hydroxytryptamine (5-HT) neurons with different serotonergic agents, such as l-tryptophan, 5-hydroxytryptophan, imipramine, fluoxetine, 5-methoxy-tryptamine, quipazine, and fenfluramine, showed the inhibiting role of the 5-HT system in FSIF. At the same time, following the results obtained in FSIF tests and locomotor activity tests, it can be inferred that the 5-HT antagonists used (methysergide, cyproheptadine, metergoline, cinnarizine, and pizotifen) do not act specifically in this model of aggression. P-Chlorophenylalanine effects on mice in FSIF also seem to be partly due to catecholaminolytic action.