Peripheral benzodiazepine receptors (pBDZr) were analyzed in lymphocyte membranes from patients with anxiety disorders (generalized anxiety disorder (GAD), n= 15; panic disorder (PD), n= 10; obsessive-compulsive disorder (OCD), n= 18), other mental disorders (n= 40) and 50 healthy controls, by the specific binding of 3H-PK11195. The number of binding sites (Bmax) was significantly decreased in groups with both GAD and OCD as compared with age-matched controls, by 45% and 25% respectively, whereas the binding affinity (Kd) was the same in all disorder and control groups. Conversely, no changes in binding capacity was observed in the other disorder groups and particularly in the one with PD. The abnormality in pBDZr observed in patients with GAD was restored to a normal value after long-term treatment with 2′-chloro-N-desmethyldiazepam, which also coincided with their recovery from anxiety. Our data suggest that the clinical heterogeneity in anxiety disorders might be related to different biological mechanisms and that lymphocyte pBDZr might be useful in demonstrating these differences.