Ozone is an important pollutant that has significant and frequently deleterious effects on plant health resulting in a reduction in cropy ields. This is due largely to oxidative damage caused either directly by ozone or by the reactive oxygen species generated by ozone. Plants possess a range of antioxidant defences to protect them against oxidative stress such as that caused by ozone and the expression of a wide-range of genes, including genes encoding important antioxidants, is altered by exposure to ozone. However, little is known about the signal transduction pathways linking the perception of ozone stress to gene expression. We have used a genomics approach to identify novel genes that respond to acute ozone stress in Arabidopsis thaliana. Initial transcript profiling studies using microarray analysis identified twenty genes which were highly up-regulated and one gene that was down-regulated by ozone treatment. Real Time RT-PCR and additional microarray analysis have subsequently confirmed this result. We have analyzed the expression of five of these genes in detail. Our studies show that the induction of all of these genes in response to oxidative stress was dependent on an increase in cytosolic free calcium and was specific to ozone. Importantly, they were not induced by other calcium-mobilizing oxidative stresses including hydrogen peroxide and cold. These data raise important questions about the mechanism by which these genes are induced by ozone and how stimulus specificity is encoded in the ozone calcium signature.