Abstract
An antigen for gel precipitation was prepared from chick embryo fibroblast cultures inoculated with the Reticuloendotheliosis virus. The specificity of the reaction was confirmed with reference Reticuloendotheliosis and Spleen necrosis sera. No precipitation reactions occurred between this antigen and Marek's disease, Newcastle disease, Infectious bronchitis, Pasteurella Multo‐cida and Haemorrhagic enteritis antisera.