For the last six years, the U.S. National Park Service, U.S. Environmental Protection Agency, and University researchers have been documenting the effects of ozone on a large number of woody and herbaceous species native to the southeastern United States. In Great Smoky Mountains National Park, (GRSM), ozone levels exhibit diel patterns at low elevations, where concentrations are low in the morning and high in the afternoon. At high elevations (>800 m), morning concentrations are much higher, and the total daily exposure is approximately twice that at the lower elevations. Putative ozone injury has been observed in the field in GRSM on 90 species, representing approximately 6% of the known flora in the Park. Surveys of foliar injury on several tree species show a general pattern of increasing frequency and amount of stipple with increasing elevation in GRSM, and in nearby Shenandoah National Park. Exposure-response studies were carried out in opentop chambers for six years with 46 species. Foliar symptoms seen in the field, were reproduced on 30 species, providing evidence that the foliar injury found in the field was probably due to ozone exposure.