Growth factors play an important role in the regulation of proliferation and differentiation of specific cell types. This is a guide to studying growth factors, from the search for and characterization of new activities, to "in vivo" analysis and molecular biology approaches such as DNA cloning. Although cytokines is included in the list of growth factors, the book avoids protocols relating specifically to cytokines and this volume should be seen as complementary to the volume "Cytokines: A Practical Approach" in the same series.