Recent identification of novel appetite-regulating hormones has revealed the complex interactions of these humoral factors in the regulation of feeding behavior in mammals. One of these hormones, ghrelin, a natural ligand of the orphan receptor GHS-R, purified from stomach, is able to stimulate growth hormone release from pituitary cells. Ghrelin is a 28 amino acid peptide containing an n-octanoylated serine 3 residue that is essential for its activity. Ghrelin stimulates appetite by acting on the hypothalamic arcuate nucleus, the region known to control food intake. As an orexigenic peptide, ghrelin is therefore an endogenous regulator of feeding behavior from the peripheral tissues to the central nervous system.