Multidrug resistance proteins such as P-glycoprotein (P-gp) are potential targets for improving the efficacy of paclitaxel (PTX), a mitotic inhibitor used in cancer chemotherapy. The selective estrogen receptor modulator toremifene (TOR) moderate P-gp was related to a drug resistance in vitro. A comparison of PTX alone with PTX+TOR in hormone-receptor-positive metastatic breast cancer patients (MBC) was conducted to determine the therapeutic value of adding TOR to a PTX regiment. Thirteen MBC patients received 80 mg/m2 PTX weekly (PTX group) and 14 MBC patients received the same weekly dose of PTX plus 120 mg/day TOR daily (PTX+TOR group). All 27 patients were repeatedly treated with a combination of PTX and TOR as long as disease progression or unmanageable severe adverse events were defined. The PTX group was compared with PTX+TOR group with respect to best overall response, response rate, clinical benefit rate, time to progression, adverse events and toxic profile of PTX and TOR. No significant difference in response rate was observed between the PTX group and the PTX+TOR group. However, clinical benefit rate and time to progression improved significantly in the PTX+TOR group in comparison with the PTX group. TOR did not significantly enhance the adverse events of PTX. These results suggested that combined treatment of PTX and TOR for MBC patients improves a patient response over PTX alone.