The combination of cisplatin (100 mg/m2) and 5-fluorouracil (5-FU) by continuous infusion (1 g/m2/day for 5 days) has been reported to produce a high response rate as neoadjuvant therapy for advanced squamous cell head and neck cancer. We sought to improve the response rate by increasing the dose of 5-FU to 1.5 g/m2/day and 2.0 g/m2/day with allopurinol modulation to reduce toxicity. The overall response rate in the 30 patients who received three courses of chemotherapy was 100% with a 50% complete response (CR) rate. A 50% CR rate was observed in patients with T3 (six of 12) and N3 (four of eight) disease. Six patients (four with CR) did not complete subsequent treatment as planned. Seven of 11 (63.6%) chemotherapy complete responders and three of 12 (25%) partial responders (one lost to follow-up) who received all planned treatment are free of disease. The major toxicity encountered was stomatitis (severe in 32%) followed by leukopenia. The maximum tolerated dose of 5-FU in this combination with allopurinol protection was 1.5 g/m2/day. Cisplatin plus high dose 5-FU does not appear to be associated with a higher CR rate than that reported with conventional doses of 5-FU and is more toxic.