Prior to the introduction of tamoxifen, diethylstilbestrol (DES) was widely used as the first-line endocrine therapy in postmenopausal women with advanced breast cancer. Since randomized trials reported that tamoxifen has a similar response rate but fewer side effects than DES, its use has declined markedly. We administered DES in a dose of 10-20 mg daily to 11 postmenopausal women with advanced breast cancer, all of whom had received previous endocrine and some cytotoxic therapy also. Four women showed tumour responses to DES (1 complete and 3 partial), 5 had stable disease, and 2 progressive disease. Amongst the patients who responded, 2 had previously been unresponsive to other endocrine treatments. Of the women with stable disease, 3 had prolonged relief of symptoms. No withdrawal responses were noted. The major side effects were nausea (severe in 2 patients, mild in 1) and cardiac failure (2 patients). We conclude that DES remains a useful, active agent in the management of advanced breast cancer in postmenopausal women, even in patients with tumours unresponsive to other endocrine therapy.