Diffuse large B-cell lymphoma (DLBCL) is an aggressive lymphoma with a 5-year survival rate of 35%-60%. Various clinical factors included in the International Prognostic Index have failed to identify the patients with DLBCL who will not benefit from the standard R-CHOP (cyclophosphamide/doxorubicin/vincristine/prednisone plus rituximab) treatment regimen. Bcl-2 has been implicated in conferring resistance to chemotherapy in non-Hodgkin's lymphoma and is therefore a candidate prognostic marker in DLBCL. To identify the correlation between Bcl-2 expression and response to rituximab-containing treatment regimens, histologic materials were analyzed from 292 elderly patients with confirmed DLBCL. Of these, 155 patients had received R-CHOP (53%) and 137 had received CHOP (47%). One hundred ninety-three patients (66%) were found to express high levels of Bcl-2 protein in > 50% of the tumor cells. Of the 193 Bcl-2-positive patients, the patients who received R-CHOP had a better 5-year overall rate than patients treated with CHOP (56% vs. 42%; P = 0.01), whereas in the patients with Bcl-2-negative disease, there was no statistically significant difference in the 5-year overall survival rates between the R-CHOP and CHOP regimens (58% vs. 52%; P = 0.6). Therefore, the addition of rituximab to the standard chemotherapy regimen seems to have overcome the Bcl-2-associated resistance to chemotherapy.