3. All subjects will undergo GH stimulation test by combination of GHRH (1 mcg/kg bolus) and arginine (0.5 gm/kg over 30', maximal dose 30 gm). Blood will be dawn at time 30', 60', 90' and 120' after the GHRH bolus injection. The GHRH+arginine test is the most widely used test to determine GH reserve in adults, independently from their age (14). Normal response is a peak serum GH > 9 ng/ml. Both GHRH and arginine are FDA-approved for this purpose, and have no significant side effects (GHRH may cause transient itching and flushing).