In our air pollution studies at The Pennsylvania State University, we have successfully used Prunus serotina (Black Cherry), Asclepias syriaca (Common Milkweed), Apocynum androsaemifolium (Spreading Dogbane), and Ailanthus altissima (Tree-of-Heaven) as ozone-sensitive bioindicators to detect phytotoxic levels of ambient ozone. However, ambient ozone concentrations have decreased in our study area, and we are seeking a more sensitive bioindicator species. We observed significant levels of ambient ozone-induced leaf injury (stipple) on native Rhus typhina (Staghorn Sumac) within a field in a central Pennsylvania, suggesting that this species might serve as a new and highly sensitive ozone bioindicator. Therefore, we conducted a preliminary survey to determine the incidence and severity of ozone-induced stipple on Staghorn Sumac. In the same location, we concurrently evaluated the level of foliar stipple on the ozone-sensitive bioindicator species listed above. Staghorn Sumac developed significantly greater ozone-induced symptoms than the other bioindicators and has potential to serve as a bioindicator to detect phytotoxic levels of ambient ozone in the eastern US.