There is a growing understanding that growth factors are of great importance for the regulation of cell multiplication and differentiation in normal development and in the adult organism of higher eukaryotes. Moreover, growth factors have adverse effects in several malignant and nonmalignant disease processes. In recent years, a number of polypeptide growth factors have been identified, purified and molecularly cloned. The effects and mechanisms of action of these growth factors have mainly been studied in cell culture systems. This book provides an update on the role of these growth factors in vivo, both in normal development and in pathological disorders. Moreover, the clinical application of growth factors is described.