Surface ozone (03) concentrations have proved to be difficult to control and regional 03 concentrations appear to be increasing in many parts of the world. Eucalyptus species are widely used as plantation trees in many regions that have Mediterranean, warm temperate and subtropical climates. An increased knowledge of the effects of tropospheric 03 on Eucalyptus trees may assist in the management of these plantations. The present study was set up to evaluate injury and measure growth reduction caused by 03 in ei_g~t Eucalyptus species. ~even month old saplings were extx~ed to diurnally varied concentrations of 26 or 172 nil "1 03 (7h mean) 7h day", 5 days in every 14 days, for 18 weeks. The plants were grown in open top field chambers fitted with rain excluders. Significant differences were found between the responses of different species. There was no visible injury or dry weight reduction in E. globulus. However 03 exposure caused a 30% weight reduction and 90% leaf injury in E. microcorys. E. gomphocephala also experienced a 30% weight reduction but no significant leaf injury. Hence Eucalyptus plantations in regions with the potential for photochenaical smog formation, such as some of the rapidly developing industrialising nations in Asia and South America, will need to consider 03 tolerance when selecting plantation trees.