In an attempt to define the activity and toxicity of low-dose aminoglutethimide plus steroid replacement in advanced breast cancer, we treated 40 patients with aminoglutethimide 500 mg/day + hydrocortisone 50 mg/day. Previous treatment consisted of additive hormones in 29 patients, oophorectomy in 8, and chemotherapy in 32. Among the 37 patients evaluable for response and toxicity, 5 objective responses (16.2%) and 20 stable diseases (54%) were noted. Toxicity, absent in 23 patients (62.1%) and mild in 14, consisted mainly of Grade I (WHO) nausea, drowsiness, cutaneous rash, and dizziness. Responders and patients with stable disease experienced a similar survival (median not reached at 22 months). Aminoglutethimide at low doses appears to be beneficial in patients refractory to conventional therapies even if the objective response rate is low.