This GeneChip probe array is a powerful tool for monitoring transcriptional regulation and antimicrobial agent response of P. aeruginosa. The array represents the annotated genome of P. aeruginosa strain PAO1 and includes 5,549 protein-coding sequences, and genes present in P. aeruginosa strains other thanPAO1. In addition, 199 probe sets are also present corresponding to all intergenic regions exceeding 600 base pairs. The selected probes have been screened against sequence homologies in the existing database of human genes.