Very-high-dose chemotherapy produces frequent complete responses in patients with metastatic breast cancer. These responses are transient in patients with disease that had relapsed following, or was refractory to, prior conventionally dosed therapy, but when used as first chemotherapy for metastatic disease or as consolidation for patients with responding cancer, a minority achieve durable complete remissions. Improvements in supportive care, especially in hematopoietic support, have resulted in a considerable reduction in the toxicity of this therapy and may allow further intensification through the use of multiple, rapidly cycled courses.