This protocol compare the efficacy of continuous infusion fluorouracil (5-FU) with weekly doxorubicin (DOX) and cyclophosphamide (CPM) to a "classical" monthly regimen of the same drugs, as a first line of treatment in metastatic breast carcinoma. The first arm of this protocol consisted of FAC: 5-FU 600 mg/m2 i.v. over 1 hour, day(d) 1, 2, 3, DOX 50 mg/m2 i.v. bolus, d1, and CPM, 400 mg/m2 i.v. bolus, d 1, 2, 3. The second arm consisted of FULON: 5-FU 250 mg/m2 per day continuously infused from d1 to d22, CPM 300 mg/m2 i.v. bolus, d1, 8, 15, 22, and DOX 15 mg/m2 i.v. bolus, day 1, 8, 15, 22. Between January 1990 and June 1993, 258 women with proven metastatic breast carcinoma were randomly assigned either to receive FAC or FULON chemotherapy regimen. Chemotherapy courses were administrated every 4 weeks for FAC regimen and every 6 weeks for FULON. Response rate (54 versus 53%), response duration (14 versus 12 months) and overall survival duration (23 versus 21 months) were not significantly different in the two regimens (FAC versus FULON). Preorative prognostic value of liver metastasis or high LDH level was slightly attenuated in patients treated by FULON. Efficacy of infusional 5-FU in metastatic breast cancer could have been lowered by weekly infusion of doxorubicin in the FULON regimen compared to monthly infusion. According to the modalities of delivery of the drugs, the two regimens seem equally effective.