A method of rocket immunoelectrophoresis based on the use of avian antiglobulin antibodies is described which permits the quantitation of IgG and IgM in human serum. The electrophoretic mobility of avian yolk immunoglobulin (IgY) and mammalian IgG is sufficiently different to obviate the need to chemically modify the antibody, for example by carbamylation. Rockets are obtained in agarose within 3–6 h in 2-( N-morpholino) ethane sulfonic acid buffer at pH 5.5 or 6.0. Avian globulins specific for human IgG and IgM were obtained easily and in large quantities from the egg yolk of hyperimmunized laying hens. The technique is also applicable to quantitation of immunoglobulins in various animal sera.