A gene probe encoding a Listeria monocytogenes delayed type hypersensitivity factor (DTH) was used for the detection of pathogenic biovars/serovars of the genus Listeria isolated from soft cheese. A total of 187 strains, isolated by plating techniques, were screened. The probe reacted with all isolated serovars of L. monocytogenes (except one 4b strain) and did not react with any of the Listeria innocua strains. Using the mouse bio-assay, as described by Kaufmann, a significant correlation was found between probe reaction and pathogenicity.