Girls with Turner Syndrome, between the ages of 10-16 years, were chosen as the study population. The study requires 3 overnight admissions to an in-patient Clinical Research Center(CRC). A baseline study is performed using stable isotope tracers of leucine, glycerol and glucose and serial blood sampling to measure protein and fat metabolism. Indirect calorimetry is used to measure substrate oxidation rates and total energy expenditure. DEXA scan is used to measure bone mineral density and body composition. Once the baseline study is complete subjects are randomly assigned to receive either estrogen orally or through a patch placed onto the skin in increasing doses changed every 2 weeks. After 6 weeks of estrogen treatment a second metabolic study, identical to the first, is performed, followed by a wash out period of 4 weeks. Subsequently, the subjects are switched to the alternate form of estrogen. At the end of 6 weeks a third and final metabolic study is repeated. All subjects continue to be on growth hormone throughout the study procedures.