In a phase II study, 66 patients with advanced breast cancer (median age 56 years; range, 28 to 75 years) were treated with paclitaxel (Taxol), 175 mg/m2 infused over 3 hours, and carboplatin (Paraplatin), dosed to attain an area under the concentration-time curve (AUC) of 6 mg x min/mL; treatment was repeated every 3 weeks. A total of 38 (58%) patients had received prior adjuvant chemotherapy, 21 with a regimen containing an anthracycline or mitoxantrone (Novantrone). As of May 1997, 295 cycles of paclitaxel-carboplatin have been administered, 248 (84%) at full dose. The relative dose intensity of paclitaxel is 0.9 (range, 0.5 to 1.2). Of the 66 patients, 8 (12%) have achieved a complete response and 27 (41%) a partial response, for a total response rate of 53%. Grade 3 to 4 toxicities have included anemia (5%), leukopenia (25%), thrombocytopenia (5%), nausea/vomiting (7%), myalgias/arthralgias (4%), allergic reaction, neurotoxicity, and infection (2% each). Alopecia has been universal. Median time to progression is 8.9 months; median survival has not yet been reached. We conclude that the combination of paclitaxel and carboplatin has significant activity in advanced breast cancer and can easily be administered on an outpatient basis with manageable toxicity.