The homeostasis established by the interaction among the central nervous system, the immune system and the endocrine system, is radically altered by prolonged comatose state following severe head trauma. This must be taken into account when deciding on therapy and rehabilitation. In a group of post-comatose patients, we studied peripheral lymphocyte subpopulations, defined by monoclonal antibodies, and delayed hypersensitivity. Our findings are indicative of an immunological impairment originating at glioneuronal level, following head trauma. Such a temporary immune deficiency may in turn affect the equilibrium between the reconstitution of the blood-brain barrier and neuronal repair activity.