Paclitaxel (Taxol; Bristol-Myers Squibb Company, Princeton, NJ) has been shown to be an effective agent in the treatment of metastatic breast carcinoma. This multicenter randomized study compared paclitaxel 175 mg/m2 given as a 3-hour infusion every 3 weeks with mitomycin 12 mg/m2 given as an intravenous infusion every 6 weeks. Eighty-one patients have been randomized, and preliminary results of a planned analysis of the first 36 evaluable patients per arm are reported. Pretreatment characteristics were well balanced between the two groups. All patients previously have received chemotherapy for metastatic disease, and half had both adjuvant therapy and chemotherapy for metastatic disease. All but one patient previously had received anthracyclines. Of the first 81 randomized patients, 72 were evaluable for response and toxicity (four never treated, five concomitant hormonotherapy). Partial responses were seen in 17% of patients in the paclitaxel arm and 6% in the mitomycin arm (P = .14). Crossover to paclitaxel therapy following progression on mitomycin achieved an objective response rate of 24% (five of 21 patients). Responses to paclitaxel therapy lasted for a median duration of 9.1 months (range, 6.2 to 12+ months). Median time to progression was significantly longer in the paclitaxel arm (3.5 months v 1.6 months; P = .026). The quality-of-life-adjusted analysis confirmed the advantage of paclitaxel therapy, even when the delay of disease progression was adjusted for important adverse events. Adverse events, most importantly neutropenia and neuropathy, were more frequently observed in the paclitaxel arm. However, patients remained on paclitaxel therapy for many more courses than did those treated in the mitomycin arm. In conclusion, paclitaxel 175 mg/m2 given as a 3-hour intravenous infusion has been demonstrated to be an active agent in the treatment of chemotherapy-refractory advanced breast cancer, even after therapy with mitomycin has failed.