An intensive treatment program was developed to achieve durable remissions in a high proportion of previously untreated patients with advanced stages of diffuse high-grade non-Hodgkin's lymphoma (NHL). Fifty-six patients (15-68 years) received a course of F-MACHOP (5-fluorouracil, methotrexate, cytosine-arabinoside, cyclophosphamide, doxorubicin, vincristine, and prednisone) every 3-4 weeks for 6 courses. Cycle active drugs were sequentially administered to expose rapidly proliferating tumor cells to the synergistic effects of these agents throughout the cell cycle. Forty-three patients achieved complete remission (77%) and 80% of the complete responders are projected to be alive and disease-free at 4 1/2 years (median follow-up 33 months). Up to 70% of all patients are predicted to be alive at 5 years. Bulky tumor, "B"-symptoms and lymphoblastic histology were poor prognostic factors, particularly when associated with clinically detectable disease after three courses. Toxicity included transitory myelodepression in most patients (2 septic deaths). This protocol provides effective and tolerable therapy for the majority of patients with advanced stages of diffuse aggressive NHL.