Calcium-aluminum exchange isotherms were generated for three common ion exchange equilibrium equations, and their implications relative to the probable effects of acid rainfall are examined. The equations examined were those of Gaines and Thomas (1953), Vanselow (1932), and Gapon (1933), using selectivity coefficients K(sub g+), K(sub v), ud K(sub gp), respectively, covering the range likely to be found in soils. These isotherms, shown as fraction Al in solution as a function of the charge fraction compensated by exchangeable Ca-2(E*ca) or Ca+2(E*ca), are affected by solution concentration but are independent of cation exchange capacity. These results are useful in predicting the changes in Ca-Al balance in soil solutions and leachates over time as a result of H2So4 and/or SO2 impacts.