Neuroendocrine studies of adolescent depression are still in their early formative years. This chapter reviews the current literature on various neuroendocrine studies in adolescent depression. It summarizes relevant physiological information about various endocrine systems and succinctly reviews selected adult findings in similar areas of investigation to highlight similarities and differences to adolescent studies in findings where they occur. Growth hormone (GH) release from the pituitary is regulated by the interplay of the neurotransmitters, either by direct hypothalamic action or through their effect on intermediate compounds such as growth hormone-releasing hormone (GHRH) or somatostatin. The hypothalamic-pituitary-growth hormone (HPGH) axis provides a good model for evaluating CNS functioning. Studies of adult depressives have shown blunted ACTH responses to CRH regardless of serum cortisol levels. Neurotransmitter regulation of melatonin secretion is complicated and not fully understood. Further research into the multiple aspects of serotonergic functioning should be a priority in future development.