Brief 200-Hz stimulation of the corticomedial amygdala (CMA) increases the aggressiveness of male Syrian golden hamsters for about 30 min; the effect peaks 10-15 min after stimulation. This effect is sensitive to stimulation amplitude and frequency. Stimulation at the parameters that reduce attack latency increases flank marking but does not affect copulation latency or general activity. Immunocytochemical analysis suggests that stimulation effects may be coupled to c-fos expression and that unilateral stimulation has bilateral effects. CMA stimulation effects appear to mimic part of the time course of behaviorally induced attack priming. The temporal persistence of aggression may result from long-term potentiation-like changes within CMA- related neural circuitry.