To establish the functional role of the nucleus accumbens (ACC) in emotionally motivated behaviors, extracellular single or multiple units were recorded from the ACC under an unanesthetized, freely moving non-operant condition in 43 cats. Then neuronal and behavioral responses to stimuli such as tones, live small animals, a human, air puffs and so on were analyzed using a videotape monitoring method. A total of 98 units were recorded from the ACC, and 34 (34.7%) of them responded to some of the stimuli. Of the 34 responded units, 5 (15%) units responded to quiet approach-provoking stimuli (appetitive stimuli), and 29 (85%) units responded to escape- or defensive attack-provoking stimuli (aversive stimuli). Although most of the units responded in an individual item-specific manner, there was no unit reacted to both the appetitive and aversive stimuli. The neuronal responses were not related to any movement or locomotion. The results were compared with those with the amygdala, and their neuronal responsiveness were shown to be quite different from each other. Although the ACC appears to be involved in the central processing of emotional behavior in some way, the role was suggested to be entirely different from that of the amygdala.