Communication between bacteria involves the accumulation of extracellular molecules called autoinducers (AI), which leads to the regulation of gene expression once a critical threshold concentration is reached. A Vibrio harveyi bioassay was used to show Salmonella enterica serovar Typhimurium produced AI-2 like activity when grown in medium with glucose and this activity was shown to involve the enzyme LuxS. So far the transcription of only a few genes in S. Typhimurium has been reported to be affected by the presence of AI-2. The aim of this study was to examine the global effect of AI-2 on the regulation of genes using S. Typhimurium SL1344 microarrays. A luxS mutant was constructed in S. Typhimurium SL1344 and using the V. harveyi bioassay was shown not to produce AI-2 like activity. RNA was isolated from cultures of SL1344 and the luxS mutant in late log phase and after labelling, hybridised to the SL1344 microarrays. Microarray data showed that the transcription of up to 9 % of the genome was altered by the deletion of luxS by more than two-fold. This included a number of genes involved in the pathogenicity of S. Typhimurium. Of great interest, a number of genes of unknown function (FUN genes) were identified that had altered transcriptional regulation in the mutant strain. In order to characterise these genes a panel of knockout mutants has been constructed and antibodies generated. These FUN genes are currently undergoing phenotypic characterisation.