The study was conducted to determine the influence of drought stress on foliar injury and yield responses of field-grown cotton. Cotton grown on Hanford coarse sandy loam at three levels of soil water in open-top chambers was exposed to seasonal 12-h O3 concentrations in Riverside, CA. At ambient O3 concentrations severely drought-stressed (SS) cotton averaged 25% foliar injury, while moderately stressed (SO) plants averaged 56%, and optimally watered (OW) plants averaged 68% foliar injury. Lint and seed yields were significantly reduced by O3 in OW and SO plots, while SS cotton showed no yield reductions, except at 0.111 microliters per liter. Yield reductions were primarily attributable to fewer numbers of bolls. The relative similarity in responses of OW and SO cotton was attributed to adaptation to drought stress by SO plants, which maintained the sensitivity of moderately stressed cotton to O3. These results suggest that low or moderate drought stress would have relatively little effect on the response of irrigated cotton to O3.