Parathyroid hormone-related peptide has recently been shown to have important functions in the control of cellular growth and differentiation. Studies using knockout and transgenic technology have played a key part in the development of our understanding of its physiological role in endochondral bone development and adult skeletal homeostasis. Acting, at least partly, through the parathyroid hormone/parathyroid hormone-related peptide receptor, parathyroid hormone-related peptide profoundly influences chondrocytic and osteogenic cell biology. Further understanding of these functions may have important implications in the pathophysiology and treatment of human skeletal disorders, including osteoporosis.