The gas ozone protects against the harmful effects of ultra-violet radiation in the stratosphere. However, in the troposphere ozone is toxic to plants and causes significant reductions in crop yields. Ozone is a reactive oxygen species (ROS) and can cause oxidative damage directly by entering stomata and interacting with cell wall and membrane components. Ozone can also form other ROS such as hydrogen peroxide and hydroxyl radicals that can cross the plasma membrane and cause further damage, leading to reduced transpiration, accelerated senescence and decreased photosynthesis. In addition, the plant itself can produce ROS, which are thought to be a component of the signalling pathway. Plants react to oxidative stress by increasing their antioxidant defences in an attempt to neutralise harmful ROS. The individual roles of several antioxidants have been extensively studied, however their regulation and interaction in planta have yet to be fully elucidated. The specificity of antioxidants and other stress-related molecules to each unique stress is also poorly understood. In this work a DNA microarray has been utilised to detect novel genes in Arabidopsis thaliana, that are regulated by ozone. Twenty genes, which are significantly up-regulated and one gene that is down-regulated by ozone treatment have been identified. Five of which have been chosen for further analysis. The expression of these genes in response to a range of ozone concentrations over time has been investigated using Real Time RT-PCR. These genes have been shown to be induced specifically in response to acute ozone stress and initial studies suggest that their expression is calciumdependent.