Hypotheses: H1- The fraction of glucose derived from gluconeogenesis is decreased and that from glycogenolysis is increased in the post-absorptive state in untreated GHD children when compared to healthy children. H2- Treatment with rhGH will not change the overall glucose turnover but will normalize the abnormal partitioning of gluconeogenesis and glycogenolysis in GHD children. H3- GH replacement will reduce urea production and increase estimates of protein synthesis, thus optimizing the availability of amino acids for growth. H4- Untreated children with GHD after an overnight fast will have an increased glucagon challenge response that will decrease after 8 weeks of treatment with rhGH.