A multicenter phase I/II trial of a human recombinant interferon beta (Betaseron; Triton Biosciences, Alameda, CA) was conducted in patients with recurrent glioblastoma and anaplastic astrocytoma in six centers between 1986 and 1988. Betaseron was given intravenously three times per week, starting at 90 x 10(6) IU per dose and escalating by 90 x 10(6) IU every 2 weeks up to a maximum dose of 540 x 10(6) per treatment. All patients had failed prior radiotherapy, and most had failed one or more courses of chemotherapy. Of the 72 patients entered into the protocol, 65 were considered assessable. Of 65 patients, 41 had glioblastoma, and 24 had anaplastic astrocytoma. Of the 65 assessable patients, 15 (23%) had an objective response (R), and 18 (28%) had stable disease (S), with a combined R and S rate of 51%. The Kaplan-Meier median time to progression was 24 weeks for the responders, 10 weeks for the nonresponders, and 23 weeks for the whole group. These results suggest that Betaseron has definite activity in recurrent gliomas, with an R + S rate of 51%. The maximum-tolerated dose (MTD) is between 180 and 360 x 10(6) IU, with neurotoxicity being the most troublesome toxicity at higher doses. Two patients died of treatment-related complication. Since most responders showed responses at the 180 x 10(6 IU dose range, further studies using a lower dose of Betaseron aimed at decreasing toxicity and allowing chronic maintenance therapy are merited.