A series of phase I and phase II studies investigating multiagent concomitant chemoradiotherapy in patients with poor-prognosis head and neck cancer have been conducted at the University of Chicago. Drug combinations initially included 5-fluorouracil (5-FU) and hydroxyurea, with the more recent addition of cisplatin; in the most recent trial, paclitaxel was substituted for cisplatin. The primary end point of these trials was definition of maximum tolerated doses in combination with radiation therapy. All radiation therapy was given concomitantly with chemotherapy on an every-other-week schedule (total dose, </=75 Gy). Maximum tolerated doses of the two-drug combination of hydroxyurea and 5-FU were defined at 1 g given orally twice daily for a total of 11 doses and 800 mg/m2/d for 5 days (by continuous intravenous infusion), respectively. When cisplatin was added to this regimen, the observed myelosuppression necessitated the addition of granulocyte colony-stimulating factor. The recommended phase II doses for the three-drug combination were cisplatin 100 mg/m2 every 28 days, 5-FU 800 mg/m2/d for 5 days, and hydroxyurea 1 g orally twice daily for 11 doses. The feasibility of administering radiation at 1.5 Gy twice daily with chemotherapy was also established, which allowed the administration of 75 Gy over 5 cycles (10 weeks). The initial review of this trial suggested substantial toxicity, particularly mucositis and myelosuppression; however, local and regional control rates also were high. Most recently, paclitaxel has replaced cisplatin in this regimen. Recommended phase II doses were hydroxyurea 0.5 g orally twice daily for 11 doses, 5-FU 600 mg/m2/d for 5 days, and paclitaxel 20 mg/m2/d for 5 days, with radiation therapy administered twice daily in 1. 5-Gy fractions. A formal phase II study of this regimen in previously untreated patients with stage IV disease has recently completed accrual and is awaiting analysis. Evaluation of a simplified paclitaxel administration schedule (1-hour infusion on day 1 of chemoradiotherapy between the two radiation fractions) is under way. In addition, the feasibility of substituting gemcitabine for hydroxyurea is undergoing evaluation. Future trials in this disease should focus on developing new combinations that are less toxic and have similar efficacy.