We report a 53-year-old-man with an aggressive Ki-1 lymphoma who had high serum CA125, a marker protein of the epithelial ovarian cancer, and interleukin-6 (IL-6) concentrations. Both CA125 and IL-6 levels decreased after chemotherapy and elevated with disease progression. The patient's lymphoma cells obtained before chemotherapy grew continuously in vitro, were IL-6 dependent and were found to secrete CA125 in culture medium. These results indicate that CA125 can be secreted by Ki-1 lymphoma cells and IL-6 may promote the growth of Ki-1 lymphoma cells.