Twenty-five women with advanced breast carcinoma refractory to first-line chemotherapy entered a phase II trial to evaluate the efficacy of ifosfamide and carboplatin. Additionally the trial assessed the clinical usefulness of oral 2-mercaptoethane sulfonate (mesna) for urothelial protection. Two partial remissions were observed (8%); toxicity was significant but acceptable, with no treatment-related deaths. The combination of ifosfamide and carboplatin had little activity as the second-line treatment in our population of patients with heavily pretreated metastatic breast cancer. Oral mesna was effective for urothelial protection, permitting outpatient administration of ifosfamide.