High-dose chemotherapy is associated with a high complete response rate and possibly some survival advantage in patients with metastatic breast cancer. We designed a clinical trial consisting of a two-step high-dose chemotherapy regimen followed by posttransplantation doxorubicin as the first chemotherapy treatment for metastatic disease. Twenty-one patients with metastatic breast cancer and no previous chemotherapy for metastatic disease were treated with high-dose cyclophosphamide (Cy; 5000 mg/m2), followed by granulocyte colony-stimulating factor. Peripheral blood stem cells were collected. Subsequently, patients received Cy (6000 mg/m2), thiotepa (500 mg/m2), and carboplatin (800 mg/m2) (CTCb) with hematopoietic rescue. Upon recovery of hematopoietic and gastrointestinal toxicity, three cycles of doxorubicin (Dox; 60 mg/m2) were delivered. After Cy, nine patients (45%) developed neutropenic fevers. There were no episodes of bacteremia. Patients received CTCb 37 days after starting Cy and had a hospital stay of 19 days. After CTCb, the median number of days to an absolute neutrophil count >5 x 10(9)/liter was 8, and the median number of days to a platelet count >20 x 10(9)/liter was 9. Neutropenic fevers occurred in 12 patients. There were no hemorrhagic complications. Fifty-five of the 63 planned courses of Dox were delivered. The median time from peripheral blood stem cell infusion to the first Dox cycle was 38 days. The median time to the second Dox cycle was 28 days, and to the last cycle was 30 days. Three episodes of neutropenic fevers were observed. Two patients developed herpes zoster. This regimen is feasible, with acceptable toxicity.