This chapter summarizes knowledge about various neuropeptides, with the greatest emphasis on the opioid neuropeptides. Pharmacological antagonism of endogenous opioids increased the level of substance P messenger RNA in the striatum, suggesting an interaction between substance P and opioid neuropeptides. Endogenous opioid peptides (EOP) neurons often contain other non-opioid neuropeptides or receptors that are important in neuroendocrine integration. EOPs were contributing to the feeding behavior in the specific experimental situations. Hypophysial portal blood contains enriched concentrations of β-endorphin, but evidence for any EOP as a hypophysiotrophic neurohormone is equivocal. Galanin is colocalized in the central nervous system (CNS) with the following neuropeptides and neurohormones: Neuropeptide Y, Cholecystokinin, growth hormone-releasing hormone, luteinizing hormone-releasing hormone, and vasopressin. Substance P in the CNS was the first of the brain-gut peptides to be discovered due to its wide distribution, but it is considered primarily as a neuropeptide without significant non-neural digestive functions.