A previous phase I study showed that in a 5-day combination of cisplatin (CDDP) 20 mg/m2/day and 5-fluorouracil (5-FU) intravenous bolus, the maximum tolerable dose of 5-FU is 200 mg/m2/day without the use of growth factors and 300 mg/m2/day with recombinant human granulocyte-monocyte colony-stimulating factor (rhGM-CSF) support. In the present phase II study, 26 patients with relapsed and/or metastatic squamous cell carcinoma of the head and neck (SCCHN) were treated with CDDP, 20 mg/m2/day, and 5-FU, 300 mg/m2/day intravenous bolus, for 5 consecutive days every 3 weeks. Granulocyte-macrophage colony-stimulating factor, 5 mg/kg/day subcutaneously, was administered from days 8 to 19. All patients had previously undergone surgery and/or radiation treatment. None had previously received chemotherapy. Mucositis (19% of the patients) and thrombocytopenia (42%) were the most frequent, but generally mild, toxicities. Relevant, GM-CSF-related side effects were detected in 12% of the patients. The median number of cycles delivered was four. Three complete and five partial responses were recorded (31% overall response rate). Further investigation of this regimen is unwarranted because of both its lack of improvement in antitumoral activity and the high costs incurred with the use of growth factors.