Heterocyclic aromatic compounds are provided which are useful in stimulating endogenous production or release of growth hormone and in treating obesity, osteoporosis (improving bone density) and in improving muscle mass and muscle strength. The heterocyclic aromatic compounds have the structure ##STR1##

including pharmaceutically acceptable salts thereof and all stereoisomers thereof, wherein X_a is heteroaryl, preferably, ##STR2##

and R₁, R_1a, R₆, Y, X_b, A, B, Z, R₃, R₄, R_4a, R₅ and R_5a are as defined herein.