A study of selected sulfur dioxide sources in Wisconsin was conducted at the request of the Enforcement Division of EPA Region V. The work done consisted of making a selection of the SO2 sources to be studied, collecting and verifying the emissions data, processing the meteorological data, using computer models to compute the ground-level concentrations of SO2, and finally analyzing the computer model output. The 55 plants initially selected for study were based on the quantity of the annual average SO2 emission. Preliminary modeling provided the basis for making the decision as to whether to do detailed modeling for each plant; detailed modeling, which provided the computed SO2 concentrations at many locations in the vicinity of each plant, was done for 34 sources, mostly power plants and paper mills. The results of the model computations indicate that air quality standards are expected to be exceeded on numerous occasions due to SO2 emissions from 7 of the 34 modeled cases. In 10 other cases, either ambient concentrations may exceed the standards on less frequent occasions, or the modeling technique does not provide a reliable basis for judgment. For the remaining plants, the resulting SO2 concentrations would be expected to remain well below the applicable standards. Other aspects of the study include: a limited model validation analysis which gave satisfactory results; preliminary study of the interactive effects of plumes from contiguous plants; and recommendations for further study of the uncertain cases mentioned above, and for cases of multiple contiguous plants.