Gaucher's disease is frequently associated with immunologic abnormalities, e.g. hypergammaglobulinemia, polyclonal gammopathy and benign monoclonal gammopathy. A patient with Gaucher's disease and a selective accumulation of IgM k in Gaucher's cells without serum monoclonal gammopathies is described. The selective accumulation is detected by immunohistochemistry analysis performed on cryostat bone marrow biopsies.