A study was made of the sexual functioning of women with metastatic breast cancer who had undergone hypophysectomy as a therapeutic measure to check the progress of the disease. The study was divided into two phases. In the first phase, 20 women, mean age 51 years, were interviewed before and after hypophysectomy with regard to their sexual functioning. In the second phase, 30 women, mean age 51 years, were studied after hypophysectomy. Emphasis was placed on three aspects of sexual behavior, i.e., desire, activity and gratification. Of the 30 women in the second phase, 23 had previously undergone mastectomy, and 7 oophorectomy; the sexual reactions to all three types of surgery were investigated. Results indicated that neither mastectomy nor oophorectomy had a significant influence on the sexual functioning of these women, whereas hypophysectomy resulted in a sharp decrease of sexual desire, activity and gratification. It was concluded that absence of the tropic pituitary hormone which activates the adrenal androgens (seemingly the only source of androgen in women) accounted for the decline in sexual functioning. This conclusion was based on the following: 1) the postoperative administration of thyroid hormones or of cortisone had no effect on the sexual status after surgery; 2) results of studies reported in the literature indicate that deprivation of ovarian hormones does not appreciably affect sexual behavior. Thus, lack of adrenal androgens appears to be the chief cause of the sharp drop in female sexual activity after hypophysectomy.