It is not clear whether hormones stimulate growth of the human fetus. Most of the hormones which exert positive effects on postnatal growth have little or no effect on fetal growth. Of those hormones which might be important physiologically, only insulin and certain insulin-like peptides have been shown to affect fetal growth. The purpose of this project is to test the hypothesis that somatomedin-C is a primary stimulator of fetal growth. The specific objectives are: 1) to study the role of somatomedin-C, insulin and other anabolic peptides on the stimulation of growth of fetal tissues in organ and cell culture, 2) to determine the site(s) of origin and the mechanisms of synthesis of somatomedin by fetal tissues, 3) to assess the physiology of somatomedin-C in the serum of the fetus and the newborn.