A monodispersed band is a dense, homogeneous band on serum protein electrophoresis (SPE), indicating the presence of a discrete protein. Minor monodispersed bands in the gamma region on SPE usually indicate minor monoclonal immunoglobulins that can be characterized by immunofixation. Occasionally, these minor monodispersed bands cannot be shown to be immunoglobulins. This report illustrates that elevated levels of C-reactive protein (CRP) may be detectable as an "M-spike" on SPE; therefore, if immunofixation is performed, anti-CRP could be included in the panel of antisera used to characterize the minor monodispersed band. The detection of CRP as an "M-spike" in the gamma region is, however, dependent upon the absence of a chelating agent in the SPE support medium. When EDTA is present, the electrophoretic mobility of CRP is altered to a beta mobility.