Danazol, an antigonadotropic agent, was administered in a dosage of 800 mg. daily for six months to 32 patients with pelvic endometriosis. Twenty-eight patients (87.5 per cent) were found to have a marked improvement of both clinical and subjective symptoms of endometriosis. Furthermore, Danazol was found to be effective in three patients with chronic cystic mastitis and one patient with fibrocystic disease. There was no change in uterine size in two patients with uterine adenomyosis and one patient with uterine myomas during the treatment period. Danazol was ineffective in relieving the symptoms of the menopausal syndrome in one patient. The main side effects of Danazol treatment were weight gain and water retention which were maximal at four months of treatment and then decreased. Other side effects such as acne, oiliness of skin, and voice change were rare in this series. Danazol therapy was found to be very effective in this study for the treatment of pelvic endometriosis, and the drug was well tolerated by the patients.