Fifteen to twenty percent of adults who suffer a traumatic brain injury (TBI) that requires hospitalization and rehabilitation have been found to have growth hormone (GH) deficiency by GH stimulation testing. Moreover, abnormalities have also been established for the cortisol and thyroid axis. The hypothesis of this proposal is that hormone replacement in TBI patients with documented abnormalities in the GH, thyroid, or cortisol axis will improve muscle function, body composition, aerobic capacity (GH) and tests of neuropsychologic function (GH, thyroid, cortisol).