A largely medial escape, hide and freeze (EHF) system has been plotted in the chick diencephalon, from which escape or freezing can be elicited peripherally as alternative responses. Supra-threshold stimulation in the core of the system yields escape mixed with freezing and hiding.The EHF system starts in the rostral anterior hypothalamus and runs back through the medial dorsal hypothalamus. A lateral extension occurs at the entry of the hypothalamic component of the occipito-mesencephalic tract. Posterior to this point the system shows a ventralward extension which does not include the putative nu. ventromedialis, but coincides instead with medial and periventricular fibres. The pre-optic area, lateral hypothalamus and mamillary area are all free of e, h and f sites.The EHF system thus corresponds well in distribution with the mammalian defensive threat-escape system. In both mammal and bird, similar behaviour is elicitable from both the diencephalic escape system and the central mesencephalic grey. The two are probably connected in the bird also by periventricular routes, some part of which can already be identified by e, h and f sites. Other properties of the EHF system, such as its role in the control of vocalisation, and its activation by non-reinforcement have been discussed elsewhere.