We conducted a multi-institutional collaborative study to examine the usefulness and safety of third-generation chemotherapy CyclOBEAP (cyclophosphamide, vincristine, bleomycin, etoposide, doxorubicin, prednisolone) combined with granulocyte colony-stimulating factor (G-CSF) in the treatment of aggressive non-Hodgkin's lymphoma (NHL). Subjects included patients with aggressive NHL who were 60 yr of age or younger and had been diagnosed as having a low-intermediate, high-intermediate, or high risk using the International Prognostic Index (IPI). A total of 24 patients were enrolled in the study between May 1997 and March 1998, including 9 low-intermediate-risk cases, 13 high-intermediate-risk cases and 2 high-risk cases. Although all 24 patients were originally enrolled in the study, one adult T-cell leukemia/lymphoma case was subsequently excluded. Thus, in the end, 23 cases were evaluated. Evaluation of the efficacy of therapy revealed complete remission in 20 patients (87%). Of these 20 patients, 8 were low-intermediate-risk cases (89%) and 12 were either high-intermediate- or high-risk cases (86%). Partial remission was achieved in 2 patients (8.7%). The 2-yr survival rate was 91.3%, and the 2-yr disease-free survival rate was 81.8%. Grade 3 or higher adverse reactions were granulocytopenia (87%), thrombocytopenia (17.4%) and liver dysfunction (4.3%). CyclOBEAP therapy has been associated with a high remission rate for aggressive NHL. When combined with G-CSF, a high relative dose intensity was maintained for each drug administered (0.94-0.97). Furthermore, although the observation period was short, both the survival rate and disease-free survival rate were good. Hence, we concluded that there were no problems associated with the procedure in terms of safety.