In the present study, we employed Affymetrix Pseudomonas aeruginosa GeneChip arrays to investigate the dynamics of global gene expression profiles during the cellular response of Pseudomonas aeruginosa to ortho-phenylphenol, which involved initial growth inhibition and metabolism. Experiment Overall Design: We conducted four independent microarray experiments (biological replicates) in the absence (control) and the presence (experimental) of ortho-phenylphenol. We calculated fold change as the ratio between the signal averages of four untreated (control) and four ortho-phenylphenol-treated (experimental) cultures for 0, 20 and 60 min exposures.