We performed a phase II trial to evaluate the efficacy and the safety of gemcitabine monotherapy, a pyrimidine antimetabolite, in patients, who had previously failed anthracycline and taxane-based chemotherapy for the treatment of metastatic breast cancer. MATERIALS AND METHODS: Twenty-one patients with metastatic breast cancer, which was unresponsive to previous chemotherapy, were entered into this study. Gemcitabine was administered at 850 mg/m2, as a 60- minute intravenous infusion on days 1, 8 and 15. This regimen was repeated every 28 days with G-CSF support, but without dose reduction. RESULTS: Objective responses were seen in 6 of the 20 patients who were able to be evaluated (1 complete response and 5 partial responses), with an objective response rate of 30%. The median time to progression was 5 (1~20) months, and the median overall survival duration was 11 (2~21) months. The actual dose intensity was 566.7 mg/m2/wk (range; 340~637.5 mg/m2/wk) and the relative dose intensity was 0.89 (range; 0.40~1.00). Toxicity was mainly hematological. Toxicities included: grade 3 neutropenia in 20% and anemia in 5%. Grades 3 and 4 thrombocytopenia occurred in 15% of the patients. CONCLUSION: Gemcitabine monotherapy is an effective and safe treatment for refractory breast cancer patients heavily treated with the anthracycline and taxane- based regimen.