Effects of exposure to SO2 at 0.5, 1.0, and 1.5 ppm for 48 hours on sulfur uptake, needle injury, height growth, diameter growth, dry weight increment, and relative growth rate of seedlings of three species of gymnosperms were investigated in a controlled environment. On the basis of such responses as needle injury, dry weight increment, relative growth rate, and diameter growth, tolerance to SO2 60 days after treatment varied in the following order:Pinus thunbergii (most tolerant),Pinus densiflora, Larix leptolepis (least tolerant). On the basis of height growth response the order of SO2 tolerance was:Pinus densiflora>Pinus thunbergii>Larix leptolepis. The range of response to SO2 of the three species varied with the specific response measured. The usefulness of relative growth rate as a pollution response is emphasized because of differences among species in initial size and growth rate. Limitations of using height growth responses to determine pollution tolerance are discussed. Caution is advised in constructing tables of pollution tolerance of plants by using data of investigators who apply different criteria for assessing plant responses to air pollution.