A number of coniferous and deciduous species that had been growing on the Suncor tailings sand dike for five to seven years were fumigated with 0.34 ppm SO2 under controlled environmental conditions. The results obtained were compared with those from similar fumigations of the same species grown in \"uncontaminated\" native soils. The coniferous species (Pinus banksiana, Picea glauca,and Picaea mariana) grown in tailings sand were much more sensitive to SO2 injury than those grown in native soils (Dystric Brunisol). They required approximately half as much fumigation time to exhibit physiological and visual injury even though they were collected less than 30 km apart. The woody angiosperms (Populus tremuloides, Caragana arborescens,and Salix sp.) were not ranked due to a pollution chamber breakdown during the experiment. No additional plant material was available to repeat this experiment.