More than 45,000 women will die of metastatic breast cancer in the United States in 1991. Endocrine therapy remains a major option for treatment of such patients, and results in complete plus partial response rates of 30% with a median duration of approximately one year. Postmenopausal status, increased age, a prolonged disease-free interval, bone and soft tissue metastases, and positive estrogen and progesterone receptors are all associated with an increased response to endocrine therapy. The use of additive hormonal therapy, specifically antiestrogens, progestins, and aromatase inhibitors, have replaced surgical ablative procedures in the majority of patients; response rates to antiestrogen therapy, progestin therapy, and aromatase inhibitors are similar, but antiestrogens have generally been associated with the most favorable therapeutic index. At present, there is no convincing evidence that either combinations of endocrine therapies or endocrine therapy combined with chemotherapy are associated with an improvement in survival for patients with metastatic disease. Future research efforts directed at defining the molecular mechanisms of endocrine activity should facilitate clinical trials of newer and potentially more effective agents. All patients with metastatic breast cancer should be considered for at least one trial of endocrine therapy provided their metastatic disease is not rapidly progressive or life-threatening.