A single radial immunodiffusion test for antibodies to Newcastle disease virus

A single radial immunodiffusion (SRD) test for the measurement of antibodies to Newcastle disease virus (NDV) is described. The test involved incorporation of concentrated intact NDV into a gel of agarose with low setting temperature and measurement of opalescent zones produced by the diffusion of antibodies to the NDV surface antigens from wells cut in the gels. With both fowl and turkey antisera the sizes of the opalescent zones showed strong correlation with the haemagglutination inhibition (HI) titres of the sera. The possible uses of the SRD test in epizootiological studies are discussed.