Corticotropin-releasing factor (CRF) produced in placenta has paracrine effects within placenta, decidua, and myometrium and endocrine effects on mother and fetus. CRF is a potent local regulator of myometrial contractility and of prostaglandin release, Recently, urocortin, a new member of the CRF family, has been localized in human placenta and membranes. Urocortin mimics some of the local effects of CRF in intrauterine tissues, that is, increase of adrenocorticotrophic hormone (ACTH) and prostagiandin release and myometrial contractility. A local CRF-BP modulates the paracrine effects of CRF and urocortin. The various CRF receptor subtypes are well distributed in placenta and membranes. CRH also acts on placental blood vasculature and has an action on fetal adrenal gland to stimulate the production of the steroid DHEA-S. In nonpregnant women, plasma CRF levels are low; they become higher during the first and second trimesters of pregnancy. A clear increase is evident at term and when CRF-BP levels decrease. Women with preterm labor show high CRF and low CRF-BP levels, supporting an involvement of this pathway in mechanism of parturition.