OBJECTIVES: I. Determine the maximum tolerated dose of intravenous irinotecan when administered weekly for 4 weeks in patients with recurrent malignant gliomas. II. Describe the pharmacokinetics of this route of administration, measuring both irinotecan and the active metabolite SN-38, and determine the effects of hepatic enzyme inducing drugs, such as anticonvulsants, on the pharmacokinetics in these patients. III. Determine preliminary response data and activity of irinotecan in this patient population. IV. Correlate response with topoisomerase I levels in brain tumor tissue from patients undergoing treatment.