Long-term inputs of acidic deposition on ridge-top, unglaciated sites in Pennsylvania have depleted many soils of adequate supplies of calcium (Ca) and magnesium (Mg). By adding limestone in 1985, Forest Service scientists desired to reduce soil acidity and the availability of potentially toxic aluminum (Al) in the soil. Soils were sampled at 3- to 5-year intervals through 2006. Calcium, Mg, and alkalinity (as measured by pH) increased from 1985 to 1996 and then remained stable through 2006 in the upper 2 inches of mineral soil. Exchangeable Al and manganese (Mn), both potentially toxic to trees, were significantly reduced by lime treatment, though effects were slower to develop at the deeper sampled depths. By 2006, Ca and Mg were significantly greater than the untreated controls even at the deepest sampled depth of 14 to 18 inches. Sugar maple foliage, also sampled in 2006, showed significantly higher Ca and Mg in samples from limed plots compared with foliage from untreated control plots. These results, and those demonstrating the benefit of liming to sugar maple, show the persistence of the added Ca and Mg in the soil system and its utilization by sugar maple 21 years after the initial application.