Antoregulation of genes is often associated with quorum sensing systems where bacteria produce and secrete molecules allow the cells to communicate with one another, leading to the activation of certain genes at certain population densities Here we describe the identification of the agr as a quorum sensing system in Staphylococcus aureus and the isolation of agr autoinducers and inhibitors by northern blotting, real time RI PCR, and beta lactamase reporter cells assays