Elucidation of the various factors controlling the pituitary gland has been a major problem of science for many years. Harris(1) has admirably reviewed the literature concerning the neural control of the hypophysis. His statement. “The pars distalis of the pituitary may in general terms be described as a gland under nervous control but lacking a nerve supply,” most aptly phrases one of the oldest problems of neuroendocrinology, and the same statement may well be extended to parts of the hypothalamico-hypophyseal system other than the pars distalis. However, a careful survey and analysis of the literature reveals that in addition to a direct neural control via nerve fibers at least three additional controlling or influencing mechanisms are known or postulated. They are: (A) a hypothalamico-hypophyseal portal system(2-5); (B) the reciprocal reactions and related functions of parts of the hypophysis to the other endocrine glands (literature too numerous to list); (C) and last, the fact that secretory materia...