Ftorafur is a 5-fluorouracil analogue which is slowly metabolized to 5-FU, resulting in prolonged therapeutic levels of this latter drug. Ninety-one evaluable patients with metastatic breast cancer were treated with Ftorafur, Adriamycin, cyclophosphamide, and BCG (ACFTOR-BCG), in an attempt to increase the effectiveness of the program or decrease its myelosuppressive toxicity. The results of this trial were compared to those previously reported with the combination of 5-FU, Adriamycin, cyclophosphamide, and BCG (FAC-BCG). Overall objective response rates were 65% and 76% for ACFTOR-BCG and FAC-BCG, respectively. Durations of response were 12 months and 14 months for ACFTOR-BCG and FAC-BCG (p = 0.53). The median survival of responders was 22 and 23.9 months, respectively. Substantial toxicity was observed with Ftorafur: nausea and vomiting severe enough to cause weight loss was observed in a substantially higher fraction of the patients treated with this drug than with 5-FU. Other side-effects, which were not observed with the 5-FU combination, were somnolence, dizziness, personality changes, tremor, ataxia, and confusion. No differences in myelosuppressive toxicity were observed between the two combinations, and the incidence of infectious complications was identical. The combination of Ftorafur, Adriamycin, cyclophosphamide and BCG did not offer any advantages with respect to increased effectiveness or reduced toxicity over the FAC-BCG regimen in breast carcinoma.