An 83-year-old male was admitted with a right pleural effusion and generalized lymphadenopathy. Serum LDH level was elevated to 801 IU/L, and the pathological diagnosis from inguinal lymph node needle biopsy was malignant lymphoma (ML) of diffuse, large cell, non-cleaved type, according to the working formulation. The surface phenotypes of the malignant cells from the pleural effusion were analyzed by a fluorescent-activated cell sorter with a panel of monoclonal antibodies (MAbs). The ML cells coexpressed antigens detected by MAbs CD10 (CALLA), CD19, CD20, CD22, CD24, CD38, Ia, c-neu and surface immunoglobulin G kappa. A high expression of NRAS p21 was also detected by cytoplasmic immunofluorescence technique. The patient died 19 days later despite a combination of chemotherapy and intensive supportive therapy. From these findings it seems that c-neu may be a prognostic indicator not only for breast cancers but also for lymphoproliferative disorders. Further accumulation of such cases is needed.