This study was designed to determine the safety and efficacy of the combination therapy of gemcitabine plus carboplatin when used as a second-line treatment in patients with metastatic breast cancer (MBC). From February 2002 to May 2003, 30 previously treated patients with adenocarcinoma of the breast received gemcitabine 1000 mg/m2 on days 1 and 8 plus carboplatin to an area under the curve (AUC) of 5 on day 1. The carboplatin dose was changed to an AUC of 4.5 because of toxicity, with cycles repeated every 3 weeks. Among 30 patients enrolled, 25 were assessable for response rate (RR). There was no complete response; 9 patients (30%) had partial response, for an overall RR of 30%. The median time to progression for the study group was 20.47 weeks (range, 8-46 weeks). Treatment-related toxicities included grade 3/4 neutropenia in 50% of patients (20% of whom had febrile neutropenia), grade 3/4 anemia in 26.6% of patients, and grade 3/4 thrombocytopenia in 30%. Eleven patients (36.67%) had grade 1 alopecia, and 1 patient (3.33%) had grade 2 alopecia. Moderate nausea was observed in 8 patients (26.67%), and vomiting occurred in 7 patients. Four patients had asthenia and 3 (10%) experienced stomatitis. Three patients discontinued treatment because of hematologic toxicity (thrombocytopenia) and 2 patients are still receiving treatment. Carboplatin plus gemcitabine is an active combination for patients with MBC despite significant but manageable hematologic toxicity.