The novel gastric hormone ghrelin, a 28-amino acid peptide, has been identified as a potent growth-hormone secretagogue. Ghrelin production is regulated by nutritional and hormonal factors. Besides stimulating growth hormone secretion, studies show that ghrelin exerts a number of central and peripheral actions such as the regulation of food intake, the control of energy balance, glucose metabolism and insulin release, cardiovascular actions, the stimulation of gastric acid secretion, and motility. The broad spectrum of biological activities associated with ghrelin continues to expand. In the future, the diverse functions of ghrelin raise the possibility of its clinical application in a large number of pathological conditions.