The authors evaluated the efficacy of neoadjuvant carboplatin chemotherapy before external-beam irradiation in patients who had histologically proven glioblastoma multiforme. Twenty-five patients were treated with carboplatin, 600 mg/m2, intravenously once every 4 weeks for a total of 4 planned cycles. External-beam irradiation (60 Gy involved field) was planned after carboplatin. Of 15 patients who had residual tumor assessable for response, seven had stable disease, six had partial responses, one had a complete response, and one had progressive disease. Two of the patients who had partial responses progressed before radiotherapy. Of 10 who had gross total resections, two progressed after 3 to 4 cycles. The median time to tumor progression was 8.4 months. Median survival was 19.2 months. Myelotoxicity and other side effects of treatment were modest. Carboplatin chemotherapy after biopsy or resection of glioblastoma multiforme before irradiation is feasible. These results warrant further clinical investigation of the role that carboplatin chemotherapy may have in the treatment of patients who have newly diagnosed glioblastoma multiforme.