Seedlings of two full-sib families of loblolly pine expressing different degrees of sensitivity to O3 were exposed to 0.05 ppm O3, 0.10 ppm NO2, and/or 0.14 ppm SO2 for 6 hr/day for 28 consecutive days. The treatments were O3, NO2, SO2 (each used alone), O3+SO2, O3+NO2, and O3+NO2+SO2. Significant growth suppressions were noted with the relatively sensitive family in all but the the NO2 alone treatments. The O3+SO2 treatment had a more significant effect than O3 alone, but adding NO2 had an inconsistent effect. Significant growth suppressions were noted for the relatively non-sensitive family only in the O3+SO2 and O3+SO2+NO2 combination treatments. Adding NO2 to O3+SO2 had a slightly stimulatory effect. The relatively sensitive pine family suffered a 30% height growth suppression versus a 14% height growth suppression for the relatively insensitive family when exposed to the 3 pollutant combination. Symptoms were noted on less than 4% of the foliage in the most severe treatments. The pollutant concentrations used in this study were below the National Ambient Air Quality Standards (NAAQS) for each pollutant.