Ten days after 5, 7-dihydroxytryptamine (5,7-DHT) administration into the median (MRN) and dorsal (DRN) raphe nuclei, preceded by nomifensine IP, an increase of post-carbachol growling response occurred. There were no differences in the amount of locomotor activity on any post-lesion day. In predatory test in a competitive situation for paired cats ten and fifteen days after 5,7-DHT administration into the MRN and DRN of submissive cats, formerly submissive animals, engage in the fight for domination after lesions. HPLC analysis showed in all lesioned groups a significant reduction of 5-HT and 5-HIAA in the hypothalamus, midbrain, amygdala and hippocampus after the MRN lesion and in the hypothalamus, amygdala, hippocampus and frontal cortex after the DRN lesion. After the MRN and DRN lesion no spontaneous aggressive behavior occurred in any cat. The results indicate that both raphe nuclei participate in the central regulation of affective and predatory aggression in the cat.