Knowledge of relationships between chronic doses of O3 and crop yield is required to set air quality standards that protect agricultural interests and to determine the need to develop resistant cultivars of sensitive species. Open-top field chamber studies have provided some information of this type for a few crop species including one western cultivar of cotton. The authors objectives were to measure relationships between chronic doses of O3 and yield of an eastern cotton cultivar and to determine whether these relationships could be affected by chronic doses of SO2. 'Stoneville 213' was exposed in open-top field chambers to five doses O3 and four doses of SO2 singly, and in all possible combinations. Exposures began when first foliar leaves were expanding and continued until final harvest. Doses of SO3 at levels greater than those occurring regionally did not significantly change cotton response to O3.