An immunoelectrophoretic method has been described for the quantitation of 4 or 5 proteins simultaneously. The method is useful for monitoring complex antigen mixtures provided proper antigen standards are employed and the antiserum is of adequate titer. Monospecific antiserum is not required for the quantitative assay. We have compared the total IgM present in purified IgM sample using the quantitative immunoelectrophoresis and optical density measurements. The value obtained was 6·84 ± 0·08 which compared well with the optical density measurement value 6·9 mg/ml. In these studies 200 μl of antiserum has been employed but adaptation to microamounts can be made. The method can also be used for the quantitation of electrophoretically separable cross reacting antigens. © 1974.