Twenty-two evaluable patients with metastatic breast cancer were treated with a combination of 4-(acridinylamino)methanesulfon-m-anisidide (AMSA) and doxorubicin. All patients but one had received prior therapy with fluorouracil, cyclophosphamide, and methotrexate. Eight patients had partial responses (36%) with a median time to treatment failure of 6 months. Two patients (9%) showed minor responses, and their times to progression were 4 and 6 months. The response rates obtained with this drug combination were similar to those observed in earlier studies using doxorubicin alone.