The effects of the relatively specific serotonergic agonists 8-OH-DPAT (5-HT1A), TFMPP (5-HT1B), and DOB (5-HT2) were studied on defensive aggressive behavior in rats using the water competition test, 8-OH-DPAT (up to 0.25 mg/kg) and TFMPP (up to 1 mg/kg) were found to be ineffective, whereas DOB (up to 0.4 mg/kg) significantly reduced aggressive behavior in this test as well as in the offensive aggression test of the resident-intruder model. These results, combined with those from other studies, suggest that stimulation of 5-HT1A, 5-HT1B, and 5-HT2 receptors reduces offensive aggression, whereas defensive aggression is only decreased by 5-HT2 stimulation.