A polymerase chain reaction (PCR) assay for the rapid and sensitive detection of the most prolific histamine former, Morganella morganii, was developed. 16S rDNA targeted PCR primers were designed, and the primer specificity and sensitivity of the PCR assay were evaluated. The 16S rDNA sequence (1,503 bp) for M. morganii showed 95% identity to those for enteric bacteria, i.e., Enterobacter spp., Klebsiella spp., Citrobacter spp., Hafnia alvei, Proteus spp., and Providencia spp. The unique primers for M. morganii were designed on the basis of the variable regions in the 16S rDNA sequence. The primers showed positive reactions with all M. morganii strains tested. However, PCR amplification was not detected when the primers were tested with other enteric or marine bacteria. When the sensitivity of the assay was evaluated, M. morganii was detected at levels ranging from 10(6) to 10(8) CFU/ml in albacore homogenate after the PCR amplification. The sensitivity of the assay was greatly improved with the enrichment of samples, and 9 CFU of M. morganii per ml of albacore homogenate was detected after 6 h of enrichment at 37 degrees C.