The methods available in the clinical laboratory for measuring serum immunoglobulins (G, A, M, and D) include radial immunodiffusion, electroimmunodiffusion and nephelometry. All these immunochemical technics require specific antisera and stable standards for reproducible and accurate results. Discrepancies between the quantity of protein measured by any of these technics and the actual chemically or physically measured quantity arise when the unknown and standard differ in molecular size, electrophoretic mobility, or antigenic valence. These differences may lead to over- or under-estimation of the quantity of immunoglobulin. Quantitation of immunoglobulins, especially in context with protein electrophoresis, does provide useful information for diagnosis and treatment of selective disorders.