1 Introduction.- 2 Plan and Program.- 3 Survey of Chemically Defined Cell Groups and Pathways.- Acetylcholine.- Monoamines.- Dopamine.- Noradrenaline.- Adrenaline.- Serotonin.- Histamine.- Amino Acids.- ?-Aminobutyric Acid.- Glutamate and Aspartate.- Glycine.- Taurine.- Gut-Brain Peptides.- Substance P.- Vasoactive Intestinal Polypeptide.- Cholecystokinin.- Neurotensin.- Hypophysiotropic Peptides.- Corticotropin-Releasing Factor.- Luteinizing Hormone-Releasing Hormone.- Somatostatin.- Thyrotropin-Releasing Hormone.- Neurohypophyseal Peptides.- Vasopressin and Oxytocin.- Pro-Opiomelanocortin Derivatives.- Corticotropin, or Adrenocorticotropic Hormone (ACTH).- ?-Lipotropin.- ?-Melanocyte-Stimulating Hormone.- ?-Melanocyte-Stimulating Hormone.- ?-Melanocyte-Stimulating Hormone.- ?-Endorphin.- Comment on the Functional Significance of POMC Derivatives.- Enkephalins.- Dynorphins.- Angiotensin II.- 4 Conclusions and Comments.- 5 'New' Entities in the Central Nervous System: The [Paracrine?] Core and Its Adjuncts.- 6 Classical Neuroanatomy, 'Chemical' Neuroanatomy and Neurobiology: Some Concluding Remarks.- References.