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CLINICAL CHEMISTRY, Vol. 35, No. 9, 1989 2017 Fig. 1. (top) High-resolution electrophoresis on agarose gel with beta-migrating restriction of fibrinogen in 1gMwell, and (bottom) immunofixation of plasma, showing crossreactivity of anti-IgM reagent with fibnnogen tion does not clearly identify (2). An isolated light-chain restriction should be corroborated by urine immunoelectrophoresis, and an isolated heavychain restriction should be confirmed by immunoselective serum electrophoresis (Ouchterlony method). If followup studies do not support the immunoflxation results, minor cross-reactivities of the antisera should be suspected. The location of the band on high-resolution electrophoresis can guide screening for contaminating antibodies on “monospecific” serum. Anti-fibrinogen antibodies in particular should be considered because of the hazard of misidentification of a fibrinogen band as a beta-migrating monoclonal gainniopathy.