Gonadotropin was assessed using radioimmunoassay on sera from the patients with breast cancer. Lutinizing and follicle stimulating hormones in the sera showed higher level in the breast cancer patients, who are in pre- and post-menopause, ovariectomized and adrenalectomized, than among control. Sequential changes of lutenizing and follicle stimulating hormones in the patients, who had bilateral adrenalectomies due to advanced and recurrent disease, were observed. The hormonal level rose rapidly until the 7th post-operative day, and then was kept rising gradually for one month after the operation. In patients with breast cancer, who are administered lutenizing hormone-releasing hormone, the level of follicle stimulating hormone in the sera elevated rather slowly and no marked peak as compared to healthy subjects.