OUTLINE: All patients receive modification of immunocompetence, unless rejection is present at outset. These patients proceed directly to interferon treatment. Group 1 (see Disease Characteristics): Patients receive reduced doses of their current immunosuppressive therapy for 10 days. Group 2: Patients receive reduced doses of some of their current immunosuppressive therapy and discontinue some of the other therapy for 14 days. Immunosuppressive therapy then resumes on day 15. Immunosuppressive therapy continues throughout other therapy, unless otherwise noted. Some patients may then undergo surgery or radiotherapy. Interferon therapy: Patients receive interferon alfa (IFNA) subcutaneously or intramuscularly on days 1-28 for a maximum of 3 courses. Patients then receive maintenance therapy with IFNA 3 days a week for 4 weeks for up to 6 courses. Chemotherapy (ProMACE-CytaBOM): Immunosuppressive therapy is stopped on days 1-20. Patients receive cyclophosphamide IV, doxorubicin IV, and etoposide IV over 60 minutes on day 1, oral prednisone on days 1-14, and cytarabine IV, bleomycin IV, vincristine IV, and methotrexate IV on day 8. Treatment is repeated every 21 days for up to 6 courses. Patients with positive CSF cytology receive intrathecal methotrexate or cytarabine on days 1, 3, 5, 7, and 14. Some patients may continue this therapy on day 21 , then every 3 weeks for 5 doses, or may receive cranial irradiation. Patients are followed monthly for 1 year, every 2 months for 1 year, every 4 months for 1 year, then every 6 months thereafter.