β-Endorphin (β-EP) concentrations were measured in peripheral blood mononuclear cells of 10 elderly women with major depressive disorders, 10 age- and sex-matched healthy controls and 10 young healthy controls. β-EP values were measured in resting condition and after stimulation with corticotropin-releasing hormone (CRH). In patients, β-EP values were measured in drug-free condition and after 30 days of treatment with phosphatidylserine (BCPS), 200 mg/day, p.o. Basal and CRH-stimulated β-EP concentrations were the same in patients and controls; in patients they did not change after BCPS, in spite of significant improvement of the depressive symptomato