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.sup.1, R.sup.1a, R.sup.6, X.sup.a, X.sup.b and Y 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.