Forty-six patients with progressive metastatic disease following initial response to tamoxifen therapy were treated with aminoglutethimide. Three patients (6%) achieved complete remission, 15 patients (33%) had partial response, and eight patients (17%) had stable disease. Twenty patients (44%) had progressive disease. The most common side effects were transient skin rash, lethargy, or dizziness. In four patients (7%), treatment was discontinued because of undesirable side effects within the first 2 weeks of the study. These data show that aminoglutethimide is an effective agent following tamoxifen therapy.