SummaryMitochondrial benzodiazepine receptors (MBR) are sensitive to anxiety and stress. The aim of the present study was to investigate whether platelet MBR are altered in untreated obsessive-compulsive disorder (OCD) patients and whether chronic treatment with clomipramine (CMI) regulates these receptors. MBR were assessed in 13 drug-free OCD patients as compared with 15 healthy controls. Seven of the 13 patients were treated with CMI (200–300 mg/day). The density and affinity of the receptors to their ligand [3H]PK 11195 in OCD patients and controls were not affected by the CMI treatment despite the clinical improvement. It seems that, in contrast to generalized anxiety disorder, OCD is not associated with alterations in platelet benzodiazepine receptors.