A total of 50 patients were treated weekly with 5-fluorouracil (FU), leucovorin (LV), and 4'-O-tetrahydropyranyl-doxorubicin (THP) as first-line chemotherapy for advanced breast cancer (ABC). In phase I the doses of LV (500 mg/m2, day 1) and FU (350 mg/m2, day 1) were held constant, while the dose of THP (day 1) was escalated, from the initial dose of 10 mg/m2 up to the maximum tolerated dose (MTD). Twenty-eight patients entered phase I, and MTD for THP was defined as 35 mg/m2 in this combination. Dose-limiting toxicities were myelosuppression and hepatotoxicity. In phase II, another 22 patients were treated with THP at a dose level of 30 mg/m2. Including 4 patients already treated at this dose in the first part, 25 patients were evaluable for response: 1 patient obtained a complete response (CR) and 13 showed a partial response (PR), giving an objective response rate of 56%. The median duration of response was 9.1+ months and median survival, 15.5+ months. Side effects were generally mild, with ECOG grade I and II leukopenia in 51% of all cycles and grade III in 3% of the courses. Other toxicity included nausea and vomiting (54% and 8%, respectively) and alopecia (24%), all restricted to ECOG grade I and II. Our results suggest that weekly THP/LV-FU represents an active regimen for first-line treatment of ABC with relative low toxicity.