It is demonstrated that benzodiazepine binding sites on human peripheral blood lymphocytes are the peripheral type receptors. The binding sites for the selective agonist³H-Ro 5-4864, but not for the antagonist³H-PK 11195, are completely inactivated by freezing-thawing of lymphocytes. The binding of³H-Ro 5-4864 to intact lymphocytes is activated by GABA and (+)baclofen. It is shown that the selective ligands Ro 5-4864 and PK 11195 bind to different subtypes of benzodiazepine receptors on human peripheral blood lymphocytes.