Electrophoresis of serum from a patient with multiple myeloma (an immunoglobulin-secreting tumor) shows an abnormally narrow gamma-globulin band, indicating the presence of a monoclonal (and therefore abnormal) immunoglobulin. In this example the concentration of this protein is about 18 milligrams per ml, and the "+" on the printout indicates that this value is higher than normal for gamma-globulin (range 6-17 mg/ml). In other cases such a monoclonal protein may be present at much higher concentrations.