The role of high dose therapy, including autologous stem cell transplantation (ASCT) in indolent non-Hodgkin's lymphomas remains controversial. We evaluated a dose intense regimen of CHOP induction followed by high dose cyclophosphamide consolidation (CHOP-HC) versus CHOP alone in a prospective comparison to assess intensified therapy without ASCT. Twenty-five patients with previously untreated advanced stage indolent NHL were enrolled: follicular lymphoma, grade 1 (11 patients) and grade 2 (8 patients); small lymphocytic lymphoma (5 patients); and lymphoplasmacytic lymphoma (1 patient). All patients were treated as clinically indicated. The median age was 47 years (21-70). There were 15 males, and 10 females. Three patients had intra-abdominal stage II, 2 patients with stage III, and 20 patients with stage IV disease. All patients received induction with CHOP for 4 cycles (weeks 1, 4, 7, 10): cyclophosphamide 750 mg/m2 i.v., doxorubicin 50 mg/m2 i.v., vincristine 1.4 mg/m2 i.v. (2 mg capped dose) and prednisone 100 mg p.o. x 5 days. Following induction, responding patients were given consolidation with either high dose cyclophosphamide @ 3 gm/m2 i.v. for 3 doses with G-CSF (weeks 13, 15, 17) or 2 additional cycles of CHOP (weeks 13, 16), stratified by stage and bulk of disease. The overall response rate to CHOP was 92% (3 CR, 8 PR) and to CHOP-HC was 93% (4 CR, 8 PR). The overall response, complete response and partial response rates were comparable in both arms. Median progression free survival for CHOP was 15.9 and 23.0 months for CHOP-HC. At 74.3 months median follow-up, all patients in the CHOP arm have recurred; 3 patients in the CHOP-HC arm (3 CR) have not recurred. The median overall survival has not been reached (at 5 years, 77% OS for CHOP-HC versus 83% OS for CHOP alone]. Greater hematologic toxicity was observed with CHOP-HC resulting in an increased number of hospitalizations for sepsis. There were no treatment-related deaths. No myelodysplasia or acute leukemia has been seen to date. With no obvious improvement in CR and with greater hematologic toxicity than CHOP, CHOP-HC is not recommended for treatment of indolent non-Hodgkin's lymphomas.