Three separate lines of research, initially perceived as unrelated, have converged to form the present field of the somatomedins and the insulin-like growth factors (see (1,2) for early reviews). Because these separate areas of research evolved their own terminology, there is a confusing array of names for the different factors under study. The first of these areas of research was based on the observation that a key target tissue of growth hormone in vivo responsible for the skeletal growth, namely cartilage, is not responsive to growth hormone in vitro. This tissue, however, is highly responsive to a GH-dependent factor in serum originally given the operational designation of “sulfation factor,” because it was convenient to monitor the response by measuring sulfate uptake into cartilage. Later when extracts containing this factor were shown to evoke pleiotypic responses in cartilage and certain other tissues, the less restrictive term, “somatomedin,” was introduced. Subsequent fractionations yielded thre...