Seventy-three patients under 18 years of age with a recurrent central nervous system tumor were randomized to receive combination chemotherapy with MOPP or OPP. Patients were stratified according to the tumor type into four major disease categories: (1) medulloblastoma, (2) astrocytoma and other glioma, (3) ependymoma, and (4) miscellaneous tumors to provide equal distribution of patients for each treatment within each disease category. Evaluation of response was based on computerized brain scan findings. Thirty-five patients received MOPP and 38 received OPP treatment. There were three complete and six partial remissions among patients receiving MOPP and one complete and five partial remissions among patients receiving OPP. In addition, six patients on MOPP had stable disease for seven to 21 months. Only two patients on OPP had stable disease(6 and 36 months). Most of responses in both treatment regimens occurred in patients with medulloblastoma and astrocytoma. Median duration of remission was nine months for the MOPP and 11 months for the OPP. Two patients on MOPP regimen had fatal myelosuppression. Although the more toxic MOPP regimen produced more responses than OPP in children, differences in the duration of response or survival were not statistically significant (P = .79 and P = .84, respectively).