Tropospheric concentrations of carbon dioxide ([CO₂]) and ozone ([O₃]) are increasing as a result of land-use changes and fossil fuel combustion.  These changes are hypothesized to have a large effect on water use for crops.  While leaf-level responses to elevated [CO₂] and [O₃] are well documented, few studies have addressed canopy responses to increases in these pollutants.  Evapotransporation (ET) for soybean was measured using an energy balance approach.  Plots were exposed to a 180 µmol mol^-1 increase in [CO₂], a 25% increase in ambient [O₃], or both.  Data for elevated [CO₂] and elevated [O₃] were collected throughout the 2002-2005 growing seasons and the elevated [CO₂]+[O₃] treatment was added in 2003.  Micrometeorological measurements were recorded in 10-minute intervals throughout the season for each of the treatments.  Sensible heat flux was calculated from the wind and temperature measurements.  ET was determined as a residual in the energy balance from net radiation, sensible heat flux, and soil heat flux.  The results show a general decrease in ET for all three treatments with the largest decrease observed for the plants grown in elevated [O₃] during most years.  When integrated over the entire growing season for 2002 and 2003, plants grown in elevated [CO₂] and elevated [O₃] used 10 and 18% less water, respectively.  Elevated [CO₂] showed a greater decrease in 2004 and 2005 than 2002 or 2003 which is consistent with a larger decrease in leaf level stomatal conductance measured in 2004. During 2004, when ambient [O₃] was lower, there was no effect of increases in [O₃] on ET.  While the effect of these treatments on ET are lower than observed for leaf stomatal conductance, periods with a large treatment- induced decrease in stomatal conductance result in larger decreases in ET, suggesting that stomatal conductance is strongly involved in the observed decreases in ET.