A prospective clinical trial was done to evaluate the efficacy and toxicity of cisplatin plus etoposide (VP-16) in patients with breast cancer who failed one previous chemotherapy regimen for advanced disease or relapsed within 12 months of adjuvant chemotherapy. Partial responses occurred in 11 of 44 evaluable patients (25%; 95% confidence interval (CI), 13% to 40%). The median time to disease progression in responding patients was 4 months (range, 3 to 6+ months), whereas the median time to disease progression and survival for all patients who were treated were 3 and 7 months, respectively. There was marked toxicity related to this protocol treatment including pancytopenia, gastrointestinal upset, and renal insufficiency. Two treatment-related deaths occurred; one from sepsis and one from renal failure. Thus, this regimen, as second-line chemotherapy for women with metastatic breast cancer, resulted in moderate, short-term, antitumor activity at the expense of marked toxicity.