Four cases of recurrent breast cancer effectively treated by CPT-11 were reported. These cases had undergone previous chemotherapy including adriamycin. Nevertheless, they developed no tolerance to such therapies and displayed good responsitivity to CPT-11. Effects on metastatic lesions: One was bone and three were soft tissues, was observed after the end of one course therapy. The response periods were over 210 days, 431 days, 175 days and 73 days. Thus, it was suggested that early response to drug was important clinically and was significant for enhancing the quality of life of patients. Major adverse reactions were leukopenia and gastrointestinal symptoms such as nausea, vomiting and diarrhea (Grade 2-3). However, these could be well managed by symptomatic treatment and dose modification. The results suggested that CPT-11 was an effective agent against advanced or recurrent breast cancer, and especially useful for patients who had developed a tolerance to previous therapies.