Microarray expression profiling on the model plant Arabidopsis thaliana has contributed to the elucidation of plant defence responses and resistance against disease. An Arabidopsis mutant, cir1 (constitutively induced resistance 1), previously showed enhanced resistance to the pathogenic biotrophic bacterium Pseudomonas syringae pv tomato (Pst) DC3000. It was hypothesised that induced or repressed genes in cir1 may play a role in conferring resistance against this pathogen. We investigated differential gene expression in wild type and cir1 plants without pathogen challenge using a custom 500-probe microarray, biased towards defence-response and signalling genes, to identify transcripts, which may be required for resistance in cir1. Several genes were found to be induced in cir1 at a significance threshold of −log10(p) equal to 3 (p <0.001) using a mixed model ANOVA approach. The induction of the genes encoding AtACP1 (sodium inducible calcium binding protein), AtP2C-HA (protein phosphatase 2C), AtGSTF7 (glutathione-S-transferase), tryptophan synthase beta-like and AtPAL1 (phenylalanine ammonia lyase 1) and the repression of AtEREBP-4 (ethylene response element binding protein 4) and HFR1 (long hypocotyl in far-red 1) in cir1 correlates with publicly available microarray data which shows the same genes differentially expressed in a similar manner in Arabidopsis plants infected with Pst. This observation supports our hypothesis that these genes contribute to disease resistance in cir1.