Plants produce a number of volatile organic compounds (VOCs), and this release plays a significant role in atmospheric chemistry. Although certain factors controlling the emission rates of VOCs from plants are reasonably well understood, the influence of abiotic stress, such as elevated ozone concentrations, is unknown. Therefore, the emission of VOCs from tobacco plants (Nicotiana tabacum L. cv. Bel B and Bel W3) and Scots pine (Pinus sylvestris L.) were studied in continuously stirred tank reactors under ozone exposure. A pulse treatment (5 h) with 120-170 nmol/mol ozone induced visible damages in the ozone-sensitive tobacco cv. Bel W3, while the more tolerant cv. Bel B seemed to be unaffected. The total amount and dynamics of the emission were studied. Both cultivars emitted methyl salicylate and a series of sesquiterpenes after the ozone treatment, but the response was less pronounced for Bel B plants. C 6 -volatiles that are thought to be derived from the lipoxygenase pathway were emitted only from Bel W3 plants. The results give further support to the hypothesis that the ozone-induced reactions of the ozone-sensitive Bel W3 plants resemble the hypersensitive response found after pathogen attack. Longterm ozone treatment (50 nmol/mol, 8 h/d) of pine led to 40% increased emissions of monoterpenes, while no damage was visible on the needles. Since VOCs are precursors of ozone, an increased VOC emission as a consequence of elevated ozone concentrations in the troposphere may lead to feedback mechanisms in photooxidant formation.