The peripheral benzodiazepine receptors (pbr) are present in many organs outside the brain and in glia tissue of the central nervous system. They have an essential function in steroid production and are involved in stress responses. In this paper we discuss whether the pbr could be a new biological parameter for stress, reviewing the literature that is specifically related to psychiatry. Research in various animal models as well as in humans points to correlations between pbr-density in various organs and various forms of stress. In humans correlations have been demonstrated between pbr-density on blood platelets and a number of anxiety disorders.