The relationship of hormones to pelvic tumors presents many problems of both academic and clinical interest. These can be briefly enumerated as follows: (1) Certain types of spontaneously arising neoplasms, both benign and malignant, have been suspected of resulting from hormonal dysfunction, particularly of the sex endocrine system. (2) Of much importance in this day of extensive hormonal therapy is the role which administered hormones play in inducing neoplasms. That some hormones can be carcinogenic for certain species now seems established quite clearly; that they can favor the growth of certain benign neoplasms already present is also a widely accepted concept, but whether they can produce cancer in the human female generative organs is still controversial. (3) A factor which has received increasing emphasis is the possible masking of cancer by certain symptoms, such as bleeding, which may be attributed to endocrine therapy which the patient is receiving, thus delaying early diagnosis. (4) Still a fourth problem concerns the possible use of hormones in the treatment of pelvic neoplasms. (5) Finally, there is the question as to whether there are any disturbances in the production, metabolism, or excretion of hormones which can be detected by laboratory procedures, which may prove of value in the diagnosis of neoplasms. The Gonadotrophic Hormones and Ovarian Tumors The ovary is stimulated to undergo its normal cyclic anatomic and functional changes by the gonadotrophic hormones of the pituitary; the follicle-stimulating fraction (F. S. H.) concerning itself chiefly with follicular growth and the production of estrogens, and the luteinizing fraction (L. H.) governing the development of the corpus luteum, with the formation of progesterone and additional estrogens (Fig. 1). It is not surprising, therefore, that certain dysfunctional and non-neoplastic enlargements of the ovary may arise from excessive or abnormal gonadotrophic stimulation. These may occur following even mild stimulation, if, because of damage by inflammatory or degenerative lesions, the ovary is incapable of normal response. Such enlargements frequently assume the form of small cystic degenerations of the ovary or even the production of large follicular or corpus luteum cysts. Similar lesions can be induced readily in animals with various gonadotrophic hormones and have been produced experimentally in human beings also (1). It is not at all uncommon to find such enlargements arising during the course of endocrine therapy with gonadotrophins, particularly if these are injudiciously employed. It is remarkable, however, that during pregnancy the ovary usually remains relatively unaffected by the enormous concentration of gonadotropins of placental origin, although on occasion follicular or luteal cysts may occur during gestation, especially in association with chorionepitheliomas and hydatidiform moles.