Objective　To examine whether urocortin is produced locally to regulate utero-placental vascular tone during pregnancy. Methods　We examined the distribution of urocortin in human placenta, fetal membranes and uterine tissue at term in the presence and absence of labor using a urocortin antibody produced in our laboratory and the immunoperoxidase staining method. Subsequently, we tested urocortin secretion from chorio-decidual cells in vitro using an immunoblot technique. Then， we tested whether urocortin is present in maternal plasma throughout gestation using a radioimmunoassay. A Sephadex G-50 column was used to examine whether immunoreactive urocortin (IR-urocortin) in maternal plasma is the same as synthetic urocortin. Results　IR-urocortin was observed in vascular smooth muscle of myometrium decidual stromal cells, syncytiotrophoblast and amnion epithelium. No differences in staining intensity for urocortin were detected between tissues obtained in the absence or presence of labor. Staining intensity for IR-urocortin was greatest in the decidua, suggesting this may be the main site of urocortin production. Positive staining for urocortin was observed in 40% of chorio-decidual cells with 34% of these cells secreting urocortin under basal conditions. Urocortin was detectable in maternal plasma from 16 weeks gestation and concentrations did not change as gestation progressed. IR-urocortin in the maternal plasma eluted from a Sephadex G-50 column at the same site as synthetic urocortin and had a calculated retention co-efficient of 0.44. Conclusion　This study indicates that urocortin is produced by the decidua during human pregnancy and is detectable in maternal plasma. These data are consistent with the hypothesis that urocortin is produced locally by the decidua and may act to regulate utero-placental blood flow.