Legislation-driven reductions in sulfur emissions have resulted in decreases in acid inputs to forest ecosystems of the northeastern United States in the last 10-15 years.  While there is some evidence that surface waters are beginning to respond to lower acid inputs, the rate of surface-water recovery is much less than expected.  We examined changes in the chemistry of Oa soil horizons throughout the northeastern USA, comparing samples collected in 2001-02 with samples collected in 1984 as part of the EPA's Direct/Delayed Response Program.  Oa horizons throughout the region exhibited reduced base saturation and increased exchangeable acidity between 1984 and 2001-02.  Normalized to soil carbon, the sum of exchangeable base cations (Ca, Mg, K, Na) declined from a median value of 39.2 cmol_c kg^-1 in 1984 to 18.9 cmol_c kg^-1 in 2001-02.  Median exchangeable acidity increased from 15.0 cmol_c kg^-1 to 24.3 cmol_c kg^-1 in the same period.  Acidification was most pronounced in the eastern part of the region (NH and Maine).  The continuing acidification of soils that we observed helps to explain the lower-than-expected recovery of surface waters in the region.