Docetaxel (Taxotere) belongs to a new class of anti-neoplastic agents, the taxanes. As the structurally related compound, paclitaxel, it enhances microtubule assembly and inhibits depolymerization of tubulin, thereby disrupting mitosis and cell replication. From august 1994 till december 1995, we treated thirty patients with advanced or metastatic breast cancer in a protocol aiming at evaluating the efficacy of docetaxel, administered in second, third or fourth line chemotherapy. The drug was given at a dosage of 100 mg/m2, delivered as a 1-hour infusion once every 3 weeks. Among the 30 patients, 9 (30%) showed an objective response (PR) and 15 (50%) had disease stabilization. For those 2 groups, the median time to progression was 20 weeks (range 13-61) and 13.5 weeks (range 10-37) respectively; the median survival for the whole group was 22.5 weeks (range 1-72). Myelosuppression (neutropenia) was the dose-limiting toxicity. We conclude that docetaxel is a potent single agent in heavily pretreated locally advanced or metastatic breast cancer, even in those who are resistant to an anthracycline or an anthracenedione.