Forty-three evaluable patients with advanced breast cancer were treated with a combination of mitoxantrone 10 mg/sqm and mitomycin C 10 mg/sqm every 3 weeks. Two patients (4%) achieved objective responses lasting 3 and 16 months. The median duration of survival after protocol entry was 6 months (range 1-22) and the median progression-free survival was 3.5 (range 1-20). Only mild toxicities were observed. We concluded that the mitoxantrone and mitomycin C combination has limited toxicity but low activity and only brief disease palliation in advanced breast cancer.