We developedquantitativeimmunoenzymometricassaysfor

human IgG and itssubclassesby usingmonoclonalantibod-ies, an avidin-biotindetectionsystem and, as the calibrant, the U.S. NationalReference Preparationfor SpecificHuman Proteins.The assays are sensitive (detectingas littleas 6 /L), precise (average inter-assay CV <11%), and vary linearly with concentrationsover a five- to 10-fold range, depending on the monoclonalantibody. We evaluated 22 different monoclonal antibodies, many of which remained highlyreactivewhen immobilizedin wells of microtiterplates coated with bovine serum albumin-glutaraldehydeto “cap-ture ” total IgG or subclasses of lgG in the sample. We demonstratedthe specificityof the most reactiveantibodies by usinga panelof 20 purifiedmyelomaproteins.The sumof lgG subclass concentrationscorrelated well (r = 0.84, p <0.001) with the total lgG measured in sera from 63 appar