Growth hormone secretagogues (GHSs) are artificial compounds developed to release GH in vitro. GHSs mimic an unknown endogenous factor that activates the GHS receptor in the pituitary and the hypothalamus. With the cloning of the human GHS receptor it has been demonstrated that GHS is a new physiological system that regulates GH secretion along with growth hormone-releasing factor (GHRH) and somatostatin. GHSs administered alone or in combination with GHRH are the most potent and reproducible GH releasers, and are useful tools for the diagnosis of GH deficiency when tested in a variety of pathological conditions, both in children and in adults. As therapeutic agents, they show clinical effectiveness in enhancing GH release after short-term treatment.