Growth hormone-releasing peptides and non-peptides (GHRPs, GHRP-GHS) are a new chemical class of GH secretagogues with a chemistry that ranges from small synthetic peptides to peptidomimetics. They release GH in animals and humans by a unique dual and complementary action on the hypothalamus and pituitary. Although the present GHRPs are of unnatural origin, evidence by a number of investigators is gradually accumulating to support that GHRP reflects the GH-releasing action of a new natural hypothalamic hormone yet to be isolated and identified. Despite the de novo origin of GHRP, a major reason for the persistent investigation is because of the possible practical diagnostic and therapeutic value in humans as well as the potential theoretical value of new insight into the physiological regulation of GH secretion.