Survival rates for several subgroups of patients with breast cancer treated with conventional therapy remain poor. Only about 30% of patients with primary breast cancer involving more than 9 axillary lymph nodes remain disease-free at 5 years from diagnosis despite surgery, conventional-dose chemotherapy and radiotherapy. Metastatic breast cancer with 5 year survival rates of about 3% generally represents incurable disease. Chemotherapeutic agents are conventionally limited by side effects. The easy procurement of haematopoietic stem cell support through mobilization of peripheral blood progenitors has spurred the development of new strategies employing high-dose treatment for treatment of high risk breast cancer. Autologous stem cell support antagonizes chemotherapy-induced myelotoxicity and thereby allows dose escalation by a factor of 1.5 to about 20. Pilot studies evaluating significant dose escalation in adjuvant treatment of patients with advanced disease have resulted in an apparent improvement in event-free survival rates to over 70%. Repetitive applications of chemotherapy at myeloablative doses are now increasingly being used. Data from prospectively randomized phase III trials will not be available before the end of 1998. For metastatic breast cancer one prospective, randomized clinical trial has been published. Results are significantly better for patients who have been treated by high-dose chemotherapy compared to patients who received conventional polychemotherapy (median survival 90 vs. 45 weeks). For methodological reasons (small patient numbers, patient selection, weak standard therapy etc.) results from the trials cited above are under discussion. Until publication of further results from ongoing phase III trials HDC for breast cancer remains experimental and should not be given outside of clinical trials.