From December 1995 to July 1997, six patients with primary malignant lymphoma in the central nervous system were treated with 2 to 5 cycles of the M-CHOP regimen (methotrexate 3 g/m2 on day 1, cyclophosphamide 750 mg/m2 on day 1, doxorubicin 40 mg/m2 on day 1, vincristine 1.4 mg/m2 on day 1, and predonisolone 60 mg on day 1 to 14: folic acid was given 3 hours after methotrexate at 10 mg/m2 every 3 hours for 9 doses intravenously). Five patients achieved complete remission (CR) and one experienced partial remission (PR). Posttherapeutic studies were performed in all patients with an average follow-up period of 20.1 months (range 8.1-26.8 months) after confirming the diagnosis. There was no evidence of recurrence of the tumors or growth of residual tumors in any of the patients in this period. The major toxic effect was myelosupression with leukopenia. Alopecia was observed in all patients. No treatment-related deaths were observed. The M-CHOP regimen seems to be a promising treatment for primary malignant lymphoma in the central nervous system.