Objective: To assess the effect of low-dose conjugated equine estrogens (E) on circulating neurotransmitters and the efficacy for the treatment of psychological symptoms. Design: Controlled comparative clinical study. Setting: Endocrine Research Unit, Instituto Mexicano del Seguro Social, Mexico. Patient(s): Thirty postmenopausal women received conjugated equine E. Ten women acted as a comparison group. Intervention(s): Conjugated equine E, 0.312 mg/day, for 21 days per cycle during six cycles and added chlormadinone acetate, 2 mg/day, for the last 5 days of each cycle. Green scale for climateric women and Blatt-Kupperman Menopausal Index were used for measuring psychological well-being. Main outcome measure(s): Serum levels of dopamine (DA), noradrenaline, serotonin, and beta-endorphin were quantified by specific assays at baseline and at the end of treatment. Result(s): Low baseline levels of DA, serotonin, and beta-endorphin increased significantly (P