Thirty-eight metastatic breast cancer patients were treated with aminoglutethimide. All patients had progressive metastatic disease following initial response to Tamoxifen therapy. Thirty-two patients were evaluable for response, of these, two patients (6%) had complete remission, 13 patients (41%) had partial response, and six patients (19%) had stable disease. Eleven patients (34%) had progressive disease. The most common side effects were transient skin rash, lethargy or dizziness. Four patients' (11%) treatment was discontinued because of either skin rash or dizziness within the first two weeks of the study. These data show that aminoglutethimide is an effective agent following tamoxifen therapy.