Several research groups have identified a "parathyroid hormone related peptide" (PTHrP) in tumors of patients presenting with the hypercalcemia of malignancy. The N-terminal domain of this peptide has a high degree of homology with that of the parathyroid hormone (PTH) and shares the PTH biological activities. PTHrP has later been identified in several foetal and adult normal tissues: for instance, it is expressed and secreted by foetal parathyroid glands, and it plays an important role in placental calcium transport; it is also expressed in the uterus of pregnant rats; there it could have a paracrine action on myometer relaxation. We have shown that PTHrP is present in and released in culture by foetal rat long bones. The mRNA of PTHrP is expressed in the periosteal cells of these foetal bones. The local expression and secretion of PTHrP in bone suggests that this new peptide could have a local role in the regulation of bone remodeling and development.