Fundamental to survival of living organisms is their ability to react appropri­ ately to their environment. Cannon (1929) recognized that "back of internal homeostatic mechanisms are powerful motivating agencies-appetites and hunger and thirst." Almost all observed behavior may be viewed as activity required to meet some physical or emotional need. "The higher in the scale of living things, the more numerous, the more perfect, and the more compli­ cated do these regulatory agencies become." This statement by Fredricq (1885) regarding internal mechanisms is at least as valid for behavior. Adrenal medullary secretion in preparation of "fight or flight" may be con­ sidered the first described behavioral neuroendocrine response. The conse­ quences of more prolonged stress on pituitary-adrenal cortical function and the subsequent unfolding of the means by which the brain controls the secre­ tion of the anterior and posterior pituitary glands led to the birth of neuroen­ docrinology. During the last decade, neuroendocrinology has taken a remarkable turn. Peptides which were believed at first to be involved solely in control of the pituitary by the hypothalamus were found in other areas of the brain. Other peptides were encountered in brain by their activity in competing for the high affinity binding of drugs to their receptors, and still others, first found in peripheral organs, were discovered also in brain. Perhaps even more amaz­ ing was the discovery that one or another of these peptides influence almost every aspect of behavior.