Blood cells, especially platelets and lymphocytes, are used in neuropsychiatric research as tools for investigating systemic derangements in neuropsychiatric disorders, and as peripheral models for studying central nervous system biochemistry. In the present work, we determined T lymphocyte peripheral-type benzodiazepine binding: a significant reduction of Bmax values was observed in demented patients as compared with healthy controls, whereas Kd values were similar in the two subjects' groups. A significant negative correlation was found between Bmax values and illness severity. These data, which seem to be related to an impairment of immune response and cell energy metabolism in demented patients, may represent a state-dependent marker in monitoring disease course and treatment efficacy.