A multicenter phase I-II trial of intravenous (IV) human recombinant interferon beta (rIFN-beta; Betaseron; Triton Bioscience Inc, Almeda, CA) was conducted in children with recurrent or progressive primary brain and spinal cord tumors. A total of 29 patients were enrolled: high-grade astrocytoma (12), brainstem glioma (nine), and primitive neuroectadermal tumor (three), ependymoma (two), germ cell (two), and spinal cord astrocytoma (one). Betaseron was given by IV infusion over 30 minutes 3 times per week (Monday-Wednesday-Friday [MWF]). Four dose levels were studied, and at least three patients were entered at each dose level. The treatment plan began with a three-step dose escalation for each patient over 6 weeks (initiation phase). The dose-escalation schema for the four dose levels was: 50-100-200, 100-200-400, 200-300-500, and 300-400-600 x 10(6) (M) IU/m2. Patients experiencing an objective response or stable disease after 6 weeks entered the maintenance phase at the final escalated dose, ie, 200, 400, 500, or 600 mlU/m2 (MWF). Common transient effects included chills, fever, and fatigue. Dose-limiting toxicities were hematologic, hepatic, and CNS. The maintenance maximum-tolerable dose (MTD) was 500 mlU/m2, ie, dose level 3. Response was assessed at completion of the initiation phase and at 2-month intervals during the maintenance phase. Objective partial responses were seen in patients with high-grade astrocytoma (two) and brain-stem glioma (two). Thus, four of 21 (19%) assessable patients had partial responses for a median of 4 months. Eight patients had stable disease for a median of 5+ (2 to 14+) months. Antineoplastic activity has been identified in children with high-grade astrocytomas and brainstem gliomas in a dose-intensive regimen.