In this study, 30 patients with metastatic breast cancer were treated with 5-Fluorouracil (5-FU) and high-dose Folinic acid, using a new sequential dosing schedule. Our treatment consisted of one day i.v. infusion of 500 mg/m2 of Folinic acid over two hours. One hour after the beginning of Folinic acid infusion, 5-FU (500 mg/m2) was given by i.v. bolus injection. The complete and partial response rates achieved (CR+PR) were 21% in a population of patients pretreated with chemotherapy including 5-FU. Cutaneous and bone metastasis responded best to our treatment. There were no treatment related deaths or withdrawals from the study. The drug related toxicities observed in this study were usually mild to moderate and easily controllable. Thus preliminary results of our study suggest that response rate, quality of life and time to disease progression for the responders improved by this sequential treatment.