Stomatal conductance and transpiration in cotton plants were studied in fields with different levels of ozone exposure. Higher ozone levels led to lower conductance and transpiration rates in both well-watered and water-stressed plants. The decrease in yield due to ozone exposure was closely linked to daily transpiration rates. Despite ozone stress, the stomata of the plants still responded normally to changes in light intensity. The reduced conductance and transpiration were caused by ozone hindering photosynthesis, which led to CO2 buildup in the plants.