Adolescents with anorexia nervosa (AN) are at high risk for low bone mineral density at a time when healthy adolescents are rapidly accruing bone, with implications for peak bone mass and fracture risk in later life. They are also deficient in insulin-like growth factor I (IGF-I), the bone trophic factor made in the liver in response to growth hormone (GH), despite elevated levels GH. It is possible that deficiency of IGF-I, a hormone very important for the maintenance of skeletal integrity, may contribute to the severe osteopenia seen in AN. The physiologic effects of rhIGF-I treatment in adolescents with AN had not been studied. The goal of this proposal was to investigate the acute effects of rhIGF-I on bone metabolism in adolescent girls with AN.