Purpose: This phase II study was performed to assess the response of patients with newly diagnosed, untreated malignant gliomas (anaplastic astrocytoma [AA] and glioblastoma multiforme [GBM]) to intracarotid (IC) cisplatin. Patients and Methods: Eligibility criteria included surgical intervention limited to biopsy only, measurable contrast-enhancing tumor, and unilateral tumor location within the vascular territory of one internal carotid artery. Patients were scheduled to receive four infusions of IC cisplatin (75 mg/m2 every 4 weeks) before beginning standard radiotherapy. Twenty-six patients were treated, and 22 were assessable for response. Results: Ten patients (45%) showed a greater than 25% decrease in the enhancing tumor area before radiotherapy with stabilization or improvement of neurologic deficits, and three patients (14%) had a greater than 70% decrease in tumor area. The likelihood of response to IC cisplatin was not clearly linked to patient age, tumor histology, or pretreatment tumor size. Myelosuppression, nephrotoxicity, and ototoxicity were mild. Optic neuropathy occurred in one patient, seizures in two, and fatal postinfusion cerebral edema in one. Conclusion: This study design, which permits assessment of the drug sensitivity of the untreated glioma, has shown definite antitumor activity of IC cisplatin in newly diagnosed malignant glioma patients.