PRIOR CONCURRENT THERAPY: Biologic therapy: No concurrent immunotherapy Chemotherapy: No prior mechlorethamine, vincristine, procarbazine, and prednisone (MOPP) No prior high-dose methotrexate No other concurrent chemotherapy Endocrine therapy: Not specified Radiotherapy: No concurrent radiotherapy Surgery: See Disease Characteristics Other: Recovered from acute toxic effects of any prior therapy Must be on a tyramine-free diet during procarbazine administration