Between 1977 and 1983 the Southwest Oncology Group (SWOG) evaluated chemotherapy alone (cyclophosphamide, doxorubicin, vincristine, prednisone; CHOP) or chemoimmunotherapy (CHOP-levamisole or CHOP-levamisole-BCG) in a randomized prospective clinical trial involving 715 eligible patients with all types of malignant lymphoma (ML). Of 281 evaluable patients with favorable histologic types of ML, 171 (61%) achieved complete remission (CR) and there was no difference in CR rate, CR duration, or survival according to the type of initial treatment. Of 388 evaluable patients with unfavorable histologic types of ML, 194 (50%) achieved CR. Levamisole appeared to adversely affect CR rates in nodular mixed and nodular large-cell lymphoma and CR duration in patients with unfavorable histology ML. Chemoimmunotherapy with levamisole or levamisole-BCG offers no advantage in terms of CR rates, CR duration, or survival compared to CHOP chemotherapy alone, and levamisole may have had an adverse impact on outcome in certain subtypes of ML.