Summary:Interferon was administered intravenously on 3 consecutive days each week for 3 consecutive weeks in doses escalated each week from 10 to 20 to 30 megaunits (MU)/m2/day. Nine adult patients were treated, each of whom had undergone subtotal resection of a supratentorial anaplastic glioma within 3 weeks of beginning interferon treatment. Patients ranged in age from 34 to 71 years, and Karnofsky functional scores were 70 or greater. Evaluations included neurological examination, Karnofsky functional rating, computerized tomography brain scanning, and panels of hematologic, hepatic, renal, and coagulation testing. No dose‐limiting or prohibitive toxicities were encountered, and each patient received nine interferon doses as scheduled. There were no symptoms of neurologic toxicity other than transient lethargy. Chills and fever occurred in all patients, while headache, lethargy, and back pain were experienced by half. These symptoms were most pronounced with the initial dose of each week and did not intensify with dose escalation. The most frequent side effect of interferon treatment was fever, usually peaking near the end of the initial 4‐h infusion; it became less severe during the second and third weeks. Leukopenia and granulocytopenia were mild. Serum hepatic enzyme levels rose slightly during the course of interferon treatment and returned to normal after treatment was completed. Serum interferon levels reached a maximum concentration of 2,285 U/ml at the end of infusion and were proportional to the dosage. Interferon was not detectable in lumbar cerebrospinal fluid, but fluid from the tumor bed of one patient contained 120 U/ml. All patients are being followed after having received a course of radiation therapy to the head at the completion of interferon therapy. We recommend 10‐30 MU/m2daily for 3 days as a safe initial dose of interferon for Phase II clinical trials with brain tumor patients.