OUTLINE: This is a two arm study. Patients are stratified according to prior nitrosourea administration. Patients are assigned to 1 of 2 arms, with only 1 arm being open at any time. Patients assigned to arm I receive irinotecan IV over 90 minutes on days 1, 8, 15, and 22. This is followed by a 2 week rest and continues for a maximum of 6 courses. Patients assigned to arm II receive irinotecan on day 1 every 3 weeks for up to 12 courses. Patients in both arms who received prior nitrosoureas receive reduced starting doses of irinotecan. The dosages may be increased once per patient after the first course if toxic effects are acceptable. Arm I closed as of 10/98, Arm II open as of 10/98. Patients are followed every 3 months for the first year, every 6 months for the next 4 years, then annually until death.