A case of nodular lymphocytic (centroblastic/centrocytic) lymphoma that developed within 5 months after the initial diagnosis of lymphoplasmocytic lymphoma is described. The change in the histopathological picture, consisting of the development of a functionally more differentiated B cell neoplasm, occurred in the abdominal lymph nodes while the original pattern persisted in the bone marrow, liver and spleen. The patient was also found to have a serum IgM/lambda monoclonal immunoglobulin exhibiting cold agglutinin activity with specificity for the 'non-I' erythrocyte antigens.