During the past twenty years, a great deal of experimental work has been done in attempts to clear up the mysteries surrounding the functions of the pituitary gland. Many of the problems which seemed to have been solved by the early work of Paulesco, and especially by the extensive investigations of Cushing and his associates, have been opened again by the work of Camus and Roussy and their followers, who attribute to nerve centers in the hypothalamus most of the functions which were previously proved, as it appeared, to belong to the hypophysis. Even the question whether the gland is essential to life, as believed by Paulesco and Cushing, has been denied from the start by many, including Handelsmann and Horsley, Aschner, Sweet and Allen, and more recently by Brown, and Dandy and Reichert. This paper deals with another open question: Is diabetes insipidus, which is clinically associated with tumors