This volume marks the end of twenty years of neurosecretion during which there were five symposia, namely Naples (1953), Lund (1957), Bristol (1961), Strasbourg (1966), and Kiel (1970). In comparison with these symposia an exceptionally large number of papers were read at this the sixth symposium, in London, and for economic reasons it has not been possible to publish all the papers in extenso. The editors have therefore been obliged to undertake the unenviable work of selection, a task made all the more difficult by the excel lence and importance of contributions of the symposium. We felt that it was of the utmost importance at this moment in the history of neurosecretion to present as complete a picture as possible of the present state of the subject in relation to the past and opportunities for the future. We have therefore given some preference to papers with a strong review element, research papers in areas of current importance and contributions which deal with recently developed techniques with promise for the future. We have more over attempted to strike some balance between the different areas of research on neurosecretion so that the volume as a whole may be of interest to the general reader, and that he will find in it a reasonably coherent pattern of thought which demonstrates neurosecretion as the final neuroendocrine pathway. We have attempted a certain degree of uniformity of spelling, symbols, etc.