Mass emissions of SO2, in Australia have tripled in little over a decade, to a level at which Australia is now a major source of global SO2 emissions. To examine the relationship between SO2 concentration and crop yield, five crops (wheat, soybean, peanut, navy bean and maize) were grown from the seedling stage to harvest in open top chambers under ambient climatic conditions. SO2 was introduced into the chambers for 8h/day throughout this period at concentrations of about <13, 138 or 285 μg m-3. The responses of the plants varied. Wheat and soybean were very sensitive, with yield reductions of about 5% and 25% at 135 and 275 μg m-3, respectively. Navy beans and maize were less sensitive with a yield increase of about 10% at 140 μg m-3, and unchanged yield at 285 μg m-3. Peanuts were intermediate between these categories with yield reductions of about 5% and 10% at 140 and 280 μg m-3, respectively.