A case of immunoproliferative disorder with clinical features of Waldenström's disease but with an IgG-k instead of IgM serum M component is described. The lymphocyte population in the bone marrow, blood and lymph nodes was studied by rosette test, culture with PHA and immunofluorescence staining. Most of the bone marrow lymphocytes had membrane IgG. This case represents an intermediate form between myeloma and Waldenström's disease, thus supporting the unitarian concept of all the immunoproliferative disorders.