Citrus canker is caused by Xanthomonas axonopodis pv. citri (Xac) which answer for significant economical losses in Brazilian citrus agribusiness. When the pathogen establish an intimate contact with the plant host cell, a set of pathogenicity and virulence genes are submitted to transcriptional activation mediated by a cis-regulatory motif called Plant Inducible Promoter (PIP) box. Type III secretion system (TTSS) and associated secreted effectors are controlled by HrpX dependent manner by means of PIPbox gene expression activation. With the aim of studying gene expression profiles when Xac interacts with citrus host tissue we have used a bioinformatic tool in order to map PIPbox along Xac genome. Two hundred and eight (208) genes neighboring to PIP elements were mapped and genomic clones corresponding to these genes were immobilized on a macroarray membrane in order to test for possible in vivo activation of PIP mediated expression. Probes corresponding the random amplified cDNAs from non-infecting Xac (grown on nutrient broth medium) and infecting Xac (bacteria grown 12 or 20 hours on XVM2 induction medium and recovered from host plant 3 and 5 days after inoculation) were hybridized to the macroarray. Eighty-five (85) differentially expressed genes were identified when comparing non-infecting and infecting Xac, which have been validated by semi-quantitative PCR and reporter gene expression. The differentially expressed genes can be grouped as those up-regulated or down-regulated, and patterns of temporal regulation could also be noticed. These genes can still be classed in accordance with their attributed function, so genes coding for proteins related to the metabolism of bacterial cell wall and membrane, iron acquisition, regulatory functions, type III secretion system, among others could be identified as infection-related altered gene expression genes. Possible roles for temporal modification of gene expression during pathogen::plant contact will be discussed.