Levels of atmospheric CO₂ have been increasing steadily over the last century and are projected to increase even more dramatically in the future. Soybeans (Glycine max L.) grown under elevated levels of CO₂ have larger herbivore populations than soybeans grown under ambient levels of CO₂. Increased abundance could reflect the fact that these herbivores are drawn in by increased amounts of volatiles or changes in the composition of volatiles released by plants grown under elevated CO₂ conditions. To determine impacts of elevated CO₂ on olfactory preferences, Japanese beetles (Popillia japonica Newman) and soybean aphids (Aphis glycines Matsumura) were placed in Y-tube olfactometers with a choice between ambient levels of CO₂ gas versus elevated levels of CO₂ gas or damaged and undamaged leaves and plants grown under ambient levels of CO₂ versus damaged and undamaged plants grown under elevated levels of CO₂. All plants had been grown from seeds under ambient or elevated levels of CO₂. Painted lady butterflies (Vanessa cardui L.) were placed in an oviposition chamber with a choice between plants grown under ambient and elevated levels of CO₂. A. glycines and V. cardui showed no significant preference for plants in either treatment. P. japonica showed no significant preference between ambient levels and elevated levels of CO₂ gas. There was a significant P. japonica preference for damaged plants grown under ambient CO₂ versus undamaged plants but no preference for damaged plants grown under elevated CO₂ versus undamaged plants. P. japonica also preferred damaged plants grown under elevated levels of CO₂ versus damaged plants grown under ambient levels of CO₂. This lack of preference for damaged plants grown under elevated CO₂ versus undamaged plants could be the result of the identical elevated levels of a green leaf volatile (2-hexenal) present in all foliage grown under elevated CO₂ regardless of damage status. Green leaf volatiles are typically released from damaged leaves and are used as kairomones by many herbivorous insects for host plant location. An increase in production of volatiles in soybeans grown under elevated CO₂ conditions may lead to larger herbivore outbreaks in the future.