A phase I Pediatric Oncology Group Study was performed combining 7,020 cGy hyperfractionated irradiation (117 cGy twice daily separated by 6 h) with increasing concurrent doses of cisplatin given with the intent of radiosensitization as treatment for children with newly diagnosed brain stem tumors. Cisplatin was infused over 120 h on weeks 1, 3, and 5 during a 6-week radiotherapy course. The following cisplatin dose levels were studied: (1) 50 mg/m2/120 h, (2) 75 mg/m2/120 h and (3) 100 mg/m2/120 h. Sixteen of 17 children completed therapy. One child expired after 2 days of treatment secondary to massive intratumoral hemorrhage. At cisplatin dose level 3 (100 mg/m2/120 h), grade 2-4 myelosuppression was encountered in 3 of 5 evaluable patients. Otherwise, no other excessive toxicities, including renal and ototoxicity, were noted.