Samples of organic surface horizons (Oi, Oe, Oa) from New York State forest soils were equilibrated with 0 to 20 cmol HNO3 Kg(-1) soil in the laboratory by a batch technique designed to simulate reactions of acid precipitation with forest floors. Each organic horizon retained a constant percentage of added H(1+)(67-96%) regardless of quantity added and buffer capacities of the samples ranged from 18 to 36 cmol (H+)kg-1(pH unit) (-1), an order of magnitude higher than those measured in underlying mineral horizons. Calcium was the dominant cation in unacidified equilibrium solutions, and its concentration changed the most in response to acidification of the soils. Aluminum contributed <1% to total cationic charge in solution and Fe concentration decreased upon addition of up to at least 5 cmol (H+)kg-1. From 38 to 79% of H+ removed by the soils was not balanced by increased in soluble Ca, Mg, K, Mn, Fe, Zn, Al, and Cu, and buffering by soluble organic and inorganic constituents accounted for 8 to 58% of H+ removal. (Copyright (c) Journal of Environmental Quality 15:229-234, 1986.)