Parathyroid hormone-related protein (PTHrP), the major factor responsible for hypercalcaemia of malignancy, is widely expressed in normal adult and fetal tissues. In this study, the distribution of PTHrP was examined in human term placenta and membranes by immunohistochemistry using antisera to PTHrP 1-34 and 37-67. PTHrP was detected in cuboidal epithelial cells of amnion and in cytotrophoblastic cells of chorionic laeve and adherent maternal decidua. In placenta, PTHrP 1-34 was detected in the syncytiotrophoblast, while PTHrP 37-67 activity was mainly present in the brush border of the syncytiotrophoblast. This study also identified PTHrP 37-67 associated with fetal vessels of placental villi. These findings may reflect the cellular distribution of intact PTHrP or sub-fragments derived by post-translational processing. Postulated actions of PTHrP in the uteroplacental unit include transport of calcium across the placenta, stretch of membranes, inhibition of uterine contractility, growth and differentiation, and vasoregulation.