Docetaxel (Taxotere; Rhône-Poulenc Rorer, Antony, France) has demonstrated significant activity in five phase II studies as first-line chemotherapy in the treatment of metastatic breast cancer. Overall response rates range from 55.3% to 67.7%, with responses seen at all sites of disease, including lung (40%) and liver (60%). The median duration of response was 8.3 months, and the median duration of survival was 16.4 months. The dose-limiting toxicity was neutropenia. Alopecia was common but reversible. Severe hypersensitivity reactions, such as flushing, chest tightness, dyspnea, or bronchospasm, were improved by corticosteroid-based premedication. Skin reactions (erythema, dermatitis) were common but generally mild, and nail toxicities (ridging, pain, onycholysis) were seldom severe. Fluid retention was dose related, but was delayed with 5-day steroid administration. Nausea, diarrhea, and vomiting were mild, as was neurotoxicity, consisting of dysesthesias in the hands and feet. Docetaxel is an active agent in the treatment of metastatic breast cancer. The level of activity as a single agent is comparable to that of most anthracycline and non-anthracycline combination chemotherapy regimens. Its activity does not appear to be affected by prior adjuvant chemotherapy. Further studies are ongoing to incorporate docetaxel in combination chemotherapy regimens.