Human placenta is a major source of corticotropin-releasing factor (CRF), and local effects of CRF in fetal membranes and placenta have been shown, i.e., adrenocorticotropic hormone (ACTH) and oxytocin release from cultured placental cells, as well as prostaglandin release from amnion, chorion and decidua. Two distinct CRF receptors (CRF-R1 and CRF-R2) have been characterized: CRF-R1 consists of two isoforms (CRF-R1alpha and CRF-R1beta) while CRF-R2 has at least three different splice variants (CRF-R2alpha, CRF-R2beta and CRF-R2gamma). To date, CRF-R1 receptor has been identified in human placenta and in pregnant myometrium, while no evidence for placental CRF-R2 receptor isoforms has been provided. The present study investigated whether the different isoforms of CRF-R1 and CRF-R2 receptor mRNA are expressed in fetal membranes and placenta. Tissues were collected after spontaneous vaginal delivery (38-40 weeks) or elective caesarean section (39-41 weeks). The gene expression of CRF receptors was first studied by reverse transcriptase-polymerase chain reaction (RT-PCR), and the presence of CRF-R1alpha, but not of CRF-R1beta, in human placental trophoblast, amnion/chorion and decidua was shown. In addition, among the three CRF-R2 splice variants, only CRF-R2beta mRNA was expressed by trophoblast and fetal membranes. By using in situ hybridization, CRF-R1 and CRF-R2 probes positively hybridized trophoblast and related membranes. CRF-R1 was localized in the syncytiotrophoblast cells, chorionic trophoblast and decidua with a small amount in the amnion. CRF-R2 probe mainly hybridized syncytiotrophoblast cells, but cytotrophoblast also contained discreet amounts of CRF-R2 mRNA signal. The CRF-R2 hybridization signal was also observed within the structure of the villi (blood vessels), chorionic trophoblast and decidual cells, but it was faint or absent in the amniotic epithelium. There was no significant difference in the distribution of CRF-R1 or CRF-R2 mRNA signal between placentas collected from vaginal delivery or caesarean section. The evidence that intrauterine tissues differently express CRF-R1alpha and CRF-R2beta supports possible different local roles of CRF and related peptides into intrauterine tissues during pregnancy. Copyright 2000 Harcourt Publishers Ltd.