The medial nucleus of the amygdala (am) has been implicated in a variety of social behaviors. The present experiment will test the hypothesis that the effect of am lesions on intermale aggressive behavior is due to interference with social learning processes. Small electrolytic lesions of the am had no significant effect in socially naive male rats. A marked reduction of aggressive behavior was observed in animals that were lesioned after experience with four aggressive interactions. Repeated testing suggests that these lesioned animals are unable to adapt their aggressive behavior on the basis of previous victory experience. The results are discussed in terms of social learning and memory processes in relation to the afferent and efferent connections of the am.