Aims: This paper reports on a new putative enterotoxin SEU encoded by the enterotoxin gene cluster egc from Staphylococcus aureus and on a real-time polymerase chain reaction (PCR) assay for detecting the seu gene. Methods and Results: PCR and sequencing revealed a new putative enterotoxin SEU encoded by some egc clusters. The seu gene resulted from sequence divergence in the psi ent1 and psi ent2 pseudogenes previously described in the egc cluster (Jarraud et al. [2001] Journal of Immunology 166, 669). The presence of the seu gene was investigated in a collection of S. aureus strains by conventional PCR and by a specific 5'-nuclease PCR assay. Among the 24 strains harbouring the egc cluster, four tested positive for the seu gene. Conclusions: The existence of the seu gene adds to the number of newly described se genes and underlines the need for a better understanding of their role in the pathogenesis of S. aureus. Significance and Impact of the Study: A thorough study of the seu gene should provide further insight into the phylogenetics of the staphylococcal enterotoxins.