In a phase II study, 77 patients with metastatic breast cancer were treated with pirarubicin, 70 mg/m2 iv every 3 weeks. Most of them had received prior hormonal (n = 39) and/or chemotherapeutic drug treatment for advanced disease, including anthracycline-containing regimens in 17. After a median of 5.5 treatment cycles (range 1-14), objective tumor response was seen in 22/71 (31%) evaluable patients (4CR, 18 PR). Stable disease occurred in 34 (48%) patients, whereas the tumor progressed in 15 (21%). Significant hematologic toxicity (WHO grade III-IV) requiring interval and/or dose adjustments was observed in 41 (58%) patients. Other treatment-related side effects were generally mild, and included alopecia in 52 (73%), nausea and/or emesis in 50 (70%), and stomatitis and diarrhea in 3 patients each. There was no treatment-related death, nor was there any evidence of cardiac toxicity thus far. In summary, the early results of this trial suggest that pirarubicin is an active and rather well tolerated drug in pretreated patients with advanced breast cancer.