The number of bioactive peptides extracted mostly from the brain and gut, but now known to be present in most organ systems, is continuously increasing [1]. These peptides include: vasoactive intestinal polypeptíde (VIP), substance P, the enkephalins, the endorphins (endogenous morphines), gastrin, cholecystokinin (CCK), motilin, gastric inhibitory polypeptide (GIP) bombesin, somatostatin, neurotensin, glucagon, pancreatic polypeptide, insulin and enteroglucagon. Immunocytochemistry has been instrumental in determining the precise localisation of regulatory peptídes in endocrine cells and also in central and peripheral neurons [2].