While employing danazol in the management of women with endometriosis, a voluntary comment patients frequently offerd was that breast pain, nodularity and premenstrual engorgement were alleviated. Because of this unexpected finding, our attention was directed to the treatment of women with mammary dysplasia, particularly fibrocystic disease of the breast. Since the incidence of mammary cancer increases rapidly with age, we obtained xerommamograms in all suspected cases to exclude such a possibility. Danazol was employed in dosages varying from 100 to 400mg per day for 3 to 6 months, depending on the severity of the disorder. More than 75% of patients experienced marked improvement or elimination of the nodularity and engorgement, and many women were spared unnecessary surgery. When surgical interference was deemed necessary in cases of multiple nodosities, danazol treatment helped to identify for biopsy a dominant nodule that did not respond to therapy. Danazol has much to offer in the treatment of benign breast disease, and represents an important advance over 'traditional' hormonal regimens proposed in the past.