Considerations of both molecular biology and data from in vitro studies suggest a potential for the combination of docetaxel (Taxotere; Rhône-Poulenc Rorer, Antony, France) with estramustine in the treatment of patients with hormone-refractory prostate cancer. Based on data from two phase I studies, the docetaxel dose recommended for phase II study in combination with estramustine in minimally and extensively pretreated patients is 70 mg/m2 and 60 mg/m2, respectively. The dose-limiting toxicity was neutropenia. In one phase I study, 63% of the 34 patients treated showed at least a 50% decline in prostate-specific antigen. An objective response was seen in 28% of patients with measurable disease, and overall median survival (22.8 months) is highly encouraging. In the second study, 82% of 17 patients showed a greater than 50% decline in prostate-specific antigen and, at the 70 mg/m2 dose level, two of six patients showed prostate-specific antigen normalization. Phase II studies have demonstrated more than 50% declines in 59% to 88% of patients treated at 70 mg/m2. Although reduction of the dose of estramustine appears to result in a somewhat lower response rate, the contribution made by estramustine to the efficacy of the estramustine/docetaxel combination must be established by randomized trials. Dexamethasone, however, does not appear to significantly contribute to the response rate of estramustine and docetaxel. Phase III studies comparing docetaxel plus estramustine with mitoxantrone plus corticosteroids are currently being planned. If the promise of docetaxel hormone-refractory prostate cancer is realized, it may be appropriate to design clinical trials that evaluate docetaxel-based regimens as adjuvant therapy in patients who are at a high risk for relapse after definitive local therapy.