Neurotransmitter ligand binding in blood cells was assessed in borderline personality disorder (BDP) patients, testing the possibility that different biochemical endophenotypes might lie beneath a specific clinical presentation. The density of peripheral benzodiazepine receptors (PBR) and serotonin transporters were assessed in peripheral blood mononuclear cells (PBMC) and platelets, respectively, showing a decrease of both parameters. Moreover, a further significant decrease of PBR in PBMC was shown for those patients with a depressive trait. Further confirmation of the presence of different molecular endophenotypes underlying the dissimilar clinical presentations in BPD may advance our possibility of successfully treating these patients.