Directive 92/66/EEC defines the tasks of the national reference laboratory for ND. As not all avian paramyxoviruses of the serotype 1, but only those of a certain virulence are considered as causative agents of ND, the most important task is the characterization of virus isolates. This is done by serotyping with specific antisera against APMV-1 to APMV-9. By means of monoclonal antibodies lentogenic strains of the La Sota type and pigeon type viruses are detected. If this is not successful, pathogenicity is determined by sequencing of the F gene cleavage site or in animal studies.