Parathyroid hormone-related protein (PTHrP) is the agent responsible for humoral hypercalcemia of malignancy. Its pathogenic role in this syndrome is well established, and attention has focused in recent years on the elucidation of the roles played by PTHrP in normal developmental and adult physiology. This review focuses on studies of the past two years: (a) elucidation of the posttranslational processing pattern of PTHrP, the mechanisms of action of the various secretory forms of PTHrP, the role of PTHrP as an intracrine regulator of cell growth and cell death; (b) the emergence of PTHrP as a critical developmental factor in the mammary gland, epidermis, and the skeleton; and (c) the advances in understanding of the roles of PTHrP in the regulation of pancreatic islet mass, vascular smooth muscle tone and proliferation, and materno-fetal calcium transfer across the placenta.