Résumé : Monoclonal antibodies detect evident antigenic variations in NDV HN and F protein. However, the A/PMV-1 viruses can be identified by HI test using a preparation made of the combination of two different monoclonals. A primary evaluation of the pathogenicity of the isolated viruses can be made by HI test using monoclonal antibodies but needs always confirmation using conventional pathogenicity tests. © 1987 Springer-Verlag.