The MAGIC model (Cosby et al. 1985, 1986) was calibrated for East and West Glacier Lakes, two adjacent high-altitude (3200 m- 3700 m) catchments in the Medicine Bow National Forest of southern Wyoming. This model uses catchment characteristics including weathering rates, soil chemical characteristics, hydrological parameters, and precipitation amounts and composition to calculate simulated lake and stream chemistry. The simulations suggest that if precipitation were acidified to pH 4.27 with sulfuric acid, the ANC of the lakes would rapidly drop by about 30 meq/m3 . This rapid drop would be followed by a further slow decline. Assuming precipitation pH of 4.27, only West Glacier Lake dropped to an average annual ANC less than 0 or a pH of less than 5.6 within a 100-year simulation. However, at this level of precipitation acidity, very acid conditions could be expected on a seasonal basis. If the precipitation pH were lowered to 4.5, monthly average ANC values likely would not fall below 0, but shorter-term acid events might well occur. The model could only be calibrated to current soil pH when input parameters allowed for at least 60 meq/m3 of organic charge in the soil solution and when the aluminum solubility parameter was set for substantial undersaturation with respect to gibbsite. Important soil chemical characteristics can, therefore, be inferred by the use of such a model.