Ozone is a phytotoxic air pollutant causing oxidative stress. We studied the effect of ozone on carotenoids, chlorophylls and polyisoprenoid alcohols in three euramerican poplar clones (Populus deltoides x Populus nigra: 'Carpaccio', 'Cima' and 'Robusta'). Poplars originating from cuttings were grown for 6 weeks and exposed to ozone in fumigation chambers (120 ppb each day for 13h). Leaf samples were collected 2, 4, 11, 15 and 17 days after the start of ozone treatment. Chemical analyses were made by HPLC-APCI-MS. The clones clearly differed in growth rate and ozone responses. 'Carpaccio' had the highest above-ground biomass, and it was also the most ozone tolerant genotype. Greatest growth reductions by ozone were measured for 'Cima ', while 'Robusta' showed the greatest number of visible injuries. Ozone and control samples were clearly separate in PCA based on analysed chemical profiles, so that ozone treatment explained 50% of the variance. Ozone reduced the concentrations of chlorophylls a and b, β-carotenes, luteins, neoxanthin and some unidentified isoprenoid derivatives in all clones. The difference between the ozone and control treatments was the strongest on the last two sampling dates. The genotypes differed from each other, but genotype explained only 12% of the variation.