Cisplatin (CDDP) and 5-fluorouracil (5-FU) have been used alone, in combination, and in various doses and sequences with radiation therapy in attempts to improve local control and survival of patients with advanced head and neck cancer. This study was undertaken to determine the toxicity and maximum tolerated dose of high-dose CDDP plus prolonged infusion 5-FU with concomitant conventional radiation therapy. Twenty-two patients with inoperable Stage III and IV squamous cell cancer were treated with CDDP (30 or 35 mg/m2 for 5 days every 4 weeks for three courses) and 5-FU (200 or 300 mg/m2 per day continuous i.v. infusion for 12 weeks) with concomitant conventional radiation therapy. This aggressive treatment regimen is accompanied by severe mucositis, myelosuppression, and chronic neuropathy. CDDP, 35 mg/m2/day x 5, and 200 mg/m2/day of 5-FU infused over 12 weeks were identified as potential doses for future Phase II studies.