The objective of this study was to compare the antitumor activity of single-agent paclitaxel (Taxol; Bristol-Myers Squibb Company, Princeton, NJ) with that of the 5-fluorouracil/doxorubicin/cyclophosphamide (FAC) combination by evaluating the extent of residual disease in the breast and regional lymph nodes of patients with breast cancer following four cycles of induction chemotherapy. Patients with histologically confirmed invasive but noninflammatory carcinoma of the breast stages T2-3, N0-1, M0 were eligible to enter the study. Patients were treated with four cycles of either FAC or single-agent paclitaxel before local therapy. Following local therapy, treatment of the two arms was identical. Of 104 operable breast cancer patients who were treated with either regimen, 78 were evaluable for response to preoperative chemotherapy and had undergone local therapy. Age, TNM classification, and estrogen receptor status of the patients were similar in the two groups. Following induction chemotherapy, the extent of disease in the breast and the distribution and number of positive nodes were similar between the two treatment arms. Disease progressed in two patients in the FAC arm and in none in the paclitaxel arm during the induction phase of therapy. A higher fraction of patients had neutropenic fever during the paclitaxel treatment. Initial data from this ongoing randomized study show that paclitaxel alone has comparable anticancer activity with FAC in patients with early breast cancer. The degree of cytoreduction was similar with both induction therapies.