Aims: The purpose of this study was to determine the global transcriptional response in a food-associated lactic acid bacterium during bile stress. Methods and Results: Clone-based DNA micro-arrays were employed to describe the global transcriptional response of Lactobacillus plantarum WCFS1 towards 0.1% porcine bile. Comparison of differential transcript profiles obtained during growth of Lact. plantarum on plates with and without bile revealed 28 and 62 putative genes, of which the expression was at least 2.5-fold up- or down-regulated by bile, respectively. Approximately, 50% of these genes appeared genetically linked, and 12 bile-responsive gene clusters were identified. Seven of the identified bile-responsive genes and gene clusters encode typical stress-related functions, including glutathione reductase and glutamate decarboxylase, involved in oxidative and acid stress, respectively. Moreover, 14 bile-responsive genes and gene clusters were identified that encode proteins that are located in the cell envelope, including the dlt operon and the F1F0 ATPase. Conclusions: The identification of a relatively high number of genes encoding cell envelope functions indicates a major impact of bile acids on the integrity and/or functionality of the cytoplasmic membrane and cell wall. Significance and Impact of the Study: The data presented here provide valuable clues towards the defence mechanisms that play a role during bile stress in Lact. plantarum.