BACKGROUND Docetaxel, a semisynthetic analog of paclitaxel, made for the needles of the European yew, Taxus baccata, is a potentially important chemotherapeutic agent for the treatment of cancer. METHODS In a phase II study patients with advanced and/or metastatic breast cancer and bidimensionally measurable disease, were treated with docetaxel 100 mg/m2 every 3 weeks as a 1 hour infusion without any premedication. Treatment was evaluated after 2 courses and every 2 subsequent courses. RESULTS Thirty-nine patients were entered, 32 were eligible. The eligible patients had a median age of 51 years (range 30-73) and a performance status WHO 1 median, (range 0-2). Twenty-eight patients had been treated with surgery, 24 with radiation. Hormonal treatment was previously given in 23, chemotherapy in 32. Of 24 patients treated as second line strategy, 13 achieved a partial remission, 1 a complete remission (overall response rate 58% (95% CI 37%-78%)). Eight patients treated as first line: 2 PR's, 1 CR. The median overall response duration was 38 weeks. The main toxicity consisted of transient grade 4 neutropenia in 149 of 167 evaluable courses (89%). However, the related infection rate was low. Re-treatment at 3 weeks, as scheduled, was nearly always possible. Other toxicities consisted of skin reactions (81%) and nail changes (41%), neurosensory toxicity (59%) and occasionally hypersensitivity reactions (16%). Fluid retention was a toxicity of major concern, observed in 59% of patients. CONCLUSIONS Docetaxel is a very active drug against breast cancer. Further studies are required to alleviate the non-hematological toxicities.