ANSWERING the invitation of the editor for a review of the work on sex-intergrades from the viewpoint of endocrinology, we propose to consider in a sweeping form the aspect of the sex-theory as it appears to the author, both in conclusion of his own work and from an open—minded consideration of all the work done upon the different aspects of the problem. In doing so, we think it will become clear wherein the endocrine aspect of the problem enters, and what are its possibilities and limitations. The more recent work upon the sex-problem started from very different viewpoints and used very different methods, the methods of cytology, genetics, teratology, physiology, serology, endocrinology, etc. The result is a vast amount of information which, if viewed critically and without prejudice in favor of any method of working or thinking, allows us, we are convinced, to assign to every single phase of that research a place within a general conception of sex. The basic problem of sex is the question why a differen...