A single high-dose cycle of chemotherapy can produce response rates in excess of 50%. However, disease-free survival (DFS) is 15-20% at 5 years. The single most important predictor of prolonged DFS is achieving a complete response (CR). Increasing the proportion of patients who achieve a complete response may improve disease-free survival. Women with metastatic breast cancer and at least a partial response (PR) to induction chemotherapy received three separate high-dose cycles of chemotherapy with peripheral blood progenitor support and G-CSF. The first intensification was paclitaxel (825 mg/m(2)), the second melphalan (180 mg/m(2)) and the third consisted of cyclophosphamide 6000 mg/m(2) (1500 mg/m(2)/day x 4), thiotepa 500 mg/m(2) (125 mg/m(2)/day x 4) and carboplatin 800 mg/m(2) (200 mg/m(2)/day x 4) (CTCb). Sixty-one women were enrolled and 60 completed all three cycles. Following the paclitaxel infusion most patients developed a reversible, predominantly sensory polyneuropathy. Of the 30 patients with measurable disease, 12 converted to CR, nine converted to a PR*, and five had a further PR, giving an overall response rate of 87%. The toxic death rate was 5%. No patient progressed on study. Thirty percent are progression-free with a median follow-up of 31 months (range 1-43 months) and overall survival is 61%. Three sequential high-dose cycles of chemotherapy are feasible and resulted in a high response rate. The challenge continues to be maintenance of response and provides the opportunity to evaluate strategies for eliminating minimal residual disease.