A prospective, randomized Phase Ilate/II trial of hyperfractionated radiation therapy was conducted: 1.2 Gy minimum tumor dose was administered twice daily with a minimum interval of 4 hr, 5 days per week. Patients with Stage III and IV carcinomas of the oral cavity, oropharynx, nasopharynx, hypopharynx, and supraglottic larynx were stratified by site, presence or absence of nodal metastases, and performance status. They were assigned to four total doses between 67.2 Gy and 81.6 Gy to all known tumors. The highest dose arm was opened after preliminary assessment indicated acceptable late morbidity rates with the three lower doses. Of 479 patients entered, 260 patients were randomized to the three lower total doses and 237 were analyzed for this preliminary report: 63 were assigned to receive 67.2 Gy, 58 to 72.0 Gy, and 116 to 76.8 Gy. Estimates of grade 4 necrosis at 2 years were 10.0%, 5.1%, and 13.9%, respectively, for patients who received total doses of 67.2 Gy, 72.0 Gy, and 76.8 Gy. There was a suggestion of a trend toward increased local control at 24 months (Kaplan-Meier estimates of 25% for 67.2 Gy, 37% for 72.0 Gy, and 42% for 76.8 Gy) (p = .08). No difference was observed in survival. Assessment of the results using Cox regression models to correct for slight inequalities of pretreatment prognostic variables supported a total dose-tumor control relationship (p = .054). Results for the lowest dose arm were comparable to previous RTOG studies of common fractionation with similar total doses. The higher local control rates with 72.0 and 76.8 Gy using hyperfractionated radiation therapy suggest an improvement in outcome with radiation therapy for advanced carcinomas of the upper aerodigestive tracts. These preliminary findings have led to a Phase III comparison of hyperfractionated radiation therapy with 1.2 Gy b.i.d. with standard fractionation.