Artificial menopause was induced by irradiation of the ovaries in 60 women suffering from carcinoma mamm˦ and its metastases. Of these, 34 women, or 56 per cent, benefited from this treatment. Typical adenocarcinoma corresponding to Grade I and II of Broder's grading are the most susceptible to this treatment. Anaplastic cancer of the breast, carcinoma simplex, corresponding to Grade III or IV of Broder's classification, were less susceptible to the œstrogen-inhibiting influence of the artificial menopause. In this group less than 1 per cent of women benefited from treatment. It is suggested that the relatively closer relationship to the normal function of the cells in the case of adenocarcinoma as compared with carcinoma simplex makes it more susceptible to the withdrawal of the œstrogenic hormone. The improvement resulting from its withdrawal suggests that this hormone stimulates growth. This improvement is temporary, but the dependence on histological type demonstrated suggests that this factor may offer more precise indications for artificial menopause as part of the management of carcinoma of the breast.