In order to specifically detect pathogenic, plasmid bearing Yersinia enterocolitica, we have developed a polymerase chain reaction (PCR) assay based on the plasmid located gene yopT. A substantial number of mismatches within the yopT coding sequence between Y. enterocolitca, Y. pseudotuberculosis, and Y. pestis was used to generate a primer pair that exclusively detects pathogenic Y. enteroco/itica with a high sensitivity and specificity. When this PCR assay was used for the detection of pathogenic Y. enterocolilica cells in artificially inoculated fecal samples and lymphoid tissue of pigs, levels as low as 102 cells per gram feces and 101 cells per gram lymphoid tissue could be detected if an 24 h pre-enrichment in Luria Bertani-Bouillon was performed prior to the PCR.