Eleven patients with malignant gliomas recurring after surgery and radiation therapy, were treated with high dose BCNU 1 050-1 200 mg/M2 with autologous bone marrow rescue. Four patients also received concomitant 5-fluorouracil 1 000 mg/M2/24 hr daily for three days. Eight of ten evaluable patients demonstrated improvement on CAT scan as well as a decrease in steroid requirement. All patients surviving longer than two weeks after BCNU administration experienced full hematologic recovery. No delayed myelosuppression was seen after a single course of high dose therapy. Two patients died as a result of therapy, one following a second induction of BCNU for a total cumulative BCNU dose of 2 400 mg/M2 and one of infection while cytopenic. Additional toxicity includes one steroid-responsive interstitial pneumonitis, one centrilobular necrosis of the liver which spontaneously resolved and one episode of deep vein thrombosis. With limitation on the maximum BCNU dose and distribution of the total dose over three days, high dose BCNU can be administered with acceptable toxicity. This approach may offer a higher response rate than that expected for standard dose BCNU.