An increase of one type of immunoglobulin referred to as macroglobulin. It differs from other immunoglobulin molecules in being five times the size of standard-sized immunoglobulin. In this disease state, B lymphocytes produce an excess amount of this type of immunoglobulin. The malignant form of the disease, a type of chronic B lymphocyte leukemia, is referred to as Waldenström's macroglobulinemia, after the Swedish hematologist who described the first cases of the disease.