The major processes by which acid deposition is neutralized in soils are cation exchange (including aluminum dynamics), sulfate adsorption, and chemical weathering. The long-term response, however, is dominated by chemical weathering, and the authors ability to predict the effect of acid deposition on chemical weathering rates is severely limited. The dissolution rates of size- and density-fractionated minerals from a soil at the Bear Brook site in Maine are similar to those of crushed 'museum' specimens, suggesting that prolonged exposure in the soil does not per se cause a decrease in weathering rate. The surface-area normalized weathering rate in the field plots appears to be a factor of 18 slower than in the lab experiments. The discrepancy might be due to an unrealistic estimate of contact time between minerals and solution, or to the inhibitory effect of high A1 concentrations on feldspar dissolution rates.