In order to study the transcriptome of the pathogen, Ehrlichia ruminantium, specific microoarray was designed and validated using genomic DNA of Gardel and Welgevonden strains. Gardel strain was isolated in Guadeloupe and Welgevonden strain in South Africa. DNA from Ehrlichia ruminantium was extracted from cell culture infected with Gardel passage 40 and Welgevonden passage 11, using QIAmp kit (Qiagen). Ehrlichia ruminantium DNA was labeled using BioPrime array CGH labeling system kit (Invitrogen) and Cy3-dCTP (Amersham). Arrays were incubated at 60°C for 20 hours in hybridization chamber. After hybridization, arrays were washed according to the Agilent protocol. Arrays were scanned and the signal intensity of all spots were quantified by Genepix pro 6.0 (Molecular Device Corporation) and data were saved for further analysis. Overall design: A one color two microarrays preliminary experiment from genomic DNA extraction.