Novel heterocyclic aromatic compounds are provided that are useful in stimulating endogenous production or release of growth hormone, said compounds having the general structure of formula I wherein R.sub.1, R.sub.1', R.sub.2, R.sub.3, R.sub.4, Xa, Y, Z and n are as described herein. The compounds provided herein are useful in treating obesity, osteoporosis (improving bone density) and in improving muscle mass and muscle strength.