Male hamsters selected for intraspecific aggressiveness were implanted with a movable monopolar electrode that was lowered through the septal region. At current levels which did not produce any motor automatisms or stereotyped competing responses, septal region stimulation prevented the initiation of subjects’ attacks on muzzled and analgesic-treated target hamsters. Thresholds for this aggression inhibition appeared to reach a minimum in the mid-and ventral septum. Stimulation at current levels necessary for aggression inhibition had no effect on sunflower seed acceptance. In operant tests, the reinforcing value of the aggression- inhibitory stimulation appeared to be positive at low current levels and negative at high levels.