In the summers of 1975, 1976, and 1977, several field investigations were carried out to determine the amounts of sulphur deposited in rain, in rain washing off trees, and by direct absorption of so2 by soil. The impact of this sulphur deposition on soils in the AOSERP study area was also determined in both field and laboratory experiments. Rain collected at several sites in 1977 was acidic, with some monthly rain samples having pH values below 5.0. The sulphur content of rain was low and there was a gradient of decreasing so4 2--s deposition in rain with increasing distance from the emission source. Scarcely, any of the sulphur in rain occurred in an acidic form. When instead the rain dripped through jack pine ~.