Thirteen patients with recurrent medulloblastoma were treated with cyclophosphamide in association with Sargramostim. Cyclophosphamide was given at doses ranging between 1.0-2.5 g/m2 daily for two doses. Sargramostim was given at a fixed dose of 250 micrograms/m2 subcutaneously twice a day beginning 24 hours after the second cyclophosphamide dose and continuing through the leukocyte nadir until the ANC was more than 1,000 cells/microliters for two consecutive days. A total of 33 courses were given with toxicity consisting of grade 4 neutropenia in all courses and grade 3-4 thrombocytopenia in 10 of 13 patients. There were no deaths related to infection or bleeding. Four patients were taken off study because of prolonged myelosuppression. Three of these patients were at the 2.5 g/m2 level, and of these three, two developed lung toxicity (grades 2 and 4, respectively). One patient developed an allergic reaction following the first injection of Sargramostim and was also taken off study. Of 10 evaluable patients, there were 9 PR and 1 SD. We conclude that cyclophosphamide at a dose of 2.0 g/m2/day x 2 days q 4 weeks in association with Sargramostim demonstrates marked activity with acceptable toxicity in patients with recurrent medulloblastoma.