The influence of soil moisture stress on crop sensitivity to O3 was evaluated for corn, cotton, soybean, and wheat grown in the United States by using yield forecasting models to estimate the influence of soil moisture deficits on regional yield and a previously developed model to predict moisture stress x O3 interactions. Reduced crop sensitivity to O3 was predicted for those regions and years for which soil moisture stress reduced yield. The models predicted a drought-induced reduction in crop sensitivity to O3 of approximately 20% for the 1979 to 1983 period; i.e., a hypothetical O3-induced yield reduction of 5% for adequately watered crops would have been reduced to a 4% effect by the 1979 to 1983 distribution of soil moisture deficits. However, predicted drought effects varied. Uncertainties in the model predictions are also discussed. (Copyright (c) 1988 Elsevier Applied Science Publishers Ltd.)