In a placebo-controlled, parallel study of 18 patients with a mean age of 20 years who had confirmed growth hormone (GH) deficiency, we evaluated body composition, insulin sensitivity, and glucose turnover at baseline (when all were receiving GH replacement); after 12 months of continued GH therapy or placebo; and after a 12-month open phase of GH therapy. In the placebo group, insulin sensitivity and fat mass increased and lipid oxidation decreased, whereas glucose oxidation increased (p