The aggressive and flight behaviour of the common marmoset monkey (Callithrix jacchus) is described and split into behavioural units, allowing analysis of agonistic behaviour evoked by electrical stimulation of the hypothalamus. The social context of the described units is also considered. C. jacchus shows clearly recognizable behavioural patterns. Free-born animals are very timid and show typical flight reactions. Within aggressive behaviour, two types of aggression can be distinguished: very violent attacks causing severe injuries, often accompanied by particular threat displays and observed during dominance and territorial encounters, and, on the other hand, relatively harmless short attacks, together with a noisy vocalization, for defensive purposes or keeping group members at a distance.