The purpose of this project is to evaluate both the early and late effects of various doses of radiation therapy on the Hypothalamic- Pituitary-Adrenal (HPA) axis; to document the effect of high dose RT on hypothalamic-pituitary-adrenal function with regard to the timing and tempo of puberty; and to determine in a subpopulation of children exposed to high dose cranial irradiation, if suppression of the progress of normal puberty with the use of GnRH agonist therapy will improve the final height attained.