To investigate the pathogenicity of Listeria spp., chick embryos were infected by two methods. Very encouraging results were obtained with the inoculation of the chorioallantoic membrane (CAM) of 10 day old chick embryos: embryos inoculated with pathogenic strains (L. monocytogenes or L. ivanovii) died within 72 h, whereas those infected with apathogenic strains survived. This test could be a suitable method to replace the mouse pathogenicity test.