Corticotropin-releasing hormone (CRH) is a key mediator of endocrine, autonomic, behavioral, and immune responses to stress. The ability of CRH to induce hormonal stress responses has been used to investigate the functionality of the hypothalamus-pituitary-adrenal axis, and consequently the activity of hypothalamic CRH neuronal systems. Indeed, CRH administration to humans causes prompt release of ACTH, followed by secretion of cortisol, aldosterone and other adrenal steroids. CRH hypersecretion/hyperactivity has been associated to major depression, anxiety-related disorders, anorexia nervosa, Alzheimer's and Parkinson's diseases and progressive supranuclear palsy. During pregnancy the human placenta and its accessory membranes are the major sites of CRH synthesis and secretion. Placental CRH secretion is autonomous, but increasing evidence indicates that maternal or fetal conditions may influence such secretion. Therefore, the emerging concept is that in the event of acute or chronic metabolic, physical or infectious stress, the placenta takes part in a stress syndrome by releasing CRH, which may contribute to restore local blood flow and to influence the timing of delivery. The CRH released by the placenta is measurable in maternal plasma and other biological fluids and may be used to diagnose subclinical processes anteceding pregnancy complications such as pre-eclampsia and preterm delivery.