Previous chemotherapy trials in hormone refractory prostate cancer have resulted in low response rates and minimal survival impact. Clearly, better agents are needed to improve outcomes in such patients. Microtubule inhibitors have been a recent focus of investigation as chemotherapeutic agents in prostate cancer; in tissue culture, docetaxel (Taxotere; Rhône-Poulenc Rorer, Collegeville, PA) appears to be the most active of these drugs. Patients enrolled in this trial had hormone refractory prostate cancer and were required to have progressive disease despite hormonal therapy and, if previously treated with antiandrogens, have progressive disease despite antiandrogen withdrawal. Patients had not been exposed to any prior chemotherapy. Testosterone suppression was continued during the trial when patients received docetaxel at 75 mg/m2 every 21 days. Thirty-five patients with ages ranging from 49 to 85 years (median age, 70 years) were enrolled in the trial. Three hundred twelve treatments have been given (median, six treatments), with a minimum follow-up of 4 months. The median prostate-specific antigen (PSA) at the time of entry was 96 ng/mL (range, 24 to 2,070 ng/mL). Seven patients (20%) have had a more than 80% decline in PSA and 16 (46%) have had a more than 50% decline. Six additional patients have had a PSA decline of 40% to 50%. Soft tissue disease was seen in 25 of 35 patients. One patient had a complete response; three others had a nearly complete response. Three patients met criteria for a partial response, yielding a 28% response rate with measurable disease. Three additional patients had substantial shrinkage and 12 had prolonged stable disease. Combining both PSA and soft tissue responses, one complete response and five partial responses were seen. Substantial responses, defined as a more than 40% PSA decline and a more than 50% reduction of bidimensional cross-products in patients with measurable disease, were seen in 17 of 35 patients enrolled. Responses were maintained for a median of 9 months (range, 2 to 24 months). The median overall survival was 27 months. Three patients remain under therapy. Toxicity remained tolerable throughout the treatment. Grade 4 toxicities requiring discontinuation of treatment included stomatitis, small bowel obstruction, and a gluteal abscess. There were two deaths during the study: one due to lung toxicity/pneumonia and one due to pulmonary embolus. The patient with lung toxicity had markedly elevated transaminases with marked involvement of the liver with tumor. Six patients stopped voluntarily due to fatigue or edema Other common toxicities were neutropenia, anemia, mild edema and hyperglycemia (due to steroids), anorexia, myalgias, and mild alopecia The responses seen in this population are very encouraging and suggest substantial durable activity for docetaxel as single-agent therapy for hormone refractory prostate cancer.