This paper presents examples of the application of ethopharmacology to the study of aggression. Low doses of benzodiazepines may increase aggression under appropriate conditions. In various animal models in male and female rats and mice the aggression enhancing effects are particularly marked when aggression is inhibited by internal or external events. It is therefore suggested that benzodiazepines have no direct effect on aggression, but modulate inhibitory factors which regulate aggression.