I. Introduction II. Contemporary Tools for Neuroendocrinological Investigation of the GH Axis A. Genetic, molecular, and transgenic models B. Human GH rhythms III. Neuropeptide Regulation of the GH Axis: Somatostatin and GHRH A. Mechanism of somatostatin actions and its receptors B. Human somatostatin receptor C. GHRH D. Feedback regulation of GH secretion IV. Other GH-Regulating Neuropeptides A. GH-releasing peptides (GHRPs) B. Galanin C. Calcitonin D. PACAP E. Opioid peptides F. TRH G. Neuropeptide Y H. Substance P I. Bombesin J. Melatonin K. Other GH secretagogues V. Neurotransmitter Regulation of GH Secretion A. Interspecies differences B. Acetylcholine and catecholamines C. Other neurotransmitters VI. Role of Metabolic Substrates in the Regulation of the GH Axis A. Blood glucose B. Leptin and FFA C. Amino acids VII. Other Hormonal Regulators of the GH Axis A. Glucocorticoids B. Gonadal sex hormones C. Thyroid hormones VIII. Regulation of the GH Axis Throughout the Human Lifetime A. Birth and infancy B. Prepuberty C. Puberty D. Adulthood E. Aging F. GH treatment in older humans IX. Exercise’s Modulation of the GH Axis A. Experimental animals B. Humans C. Neural control of GH release during exercise D. Kinetics of exercise-induced GH release X. Summary