Acid neutralization, at pH 3.0, in the mineral horizons of six acid sandy soils was measured by means of pH stat column experiments. All samples have low amounts of adsorbed base cations (0.1-4.3 mmol c kg - 1 ; base saturation 2.1-9.5%), pH ranges from 4.0 in the topsoil to 4.5 in the subsoil. The amount of NH 4 -oxalate extractable Al ranged from 87-135 mol c m - 3 in the topsoil to 171-309 mol c m - 3 in the subsoil. The total acid neutralization during a 4 week experiment ranged from 10 mol c m - 3 in the topsoil up to 198 mol c m - 3 in the subsoil. The acid neutralization rate strongly decreased in time in the first phase of the experiments. In the topsoil the acid neutralization rate became constant within a couple of days. In the subsoil samples the acid neutralization rates gradually decreased even after four weeks. These differences are strongly related to the contribution of the dissolution of NH 4 -oxalate extractable Al. The dissolution of NH 4 -oxalate extractable Al compounds accounts for 60% of the acid neutralization in the topsoil and for more than 90% of the acid neutralization in the subsoil. The dissolution rates of Al from NH 4 -oxalate extractable pools strongly decrease in time due to exhaustion of this pool. The contribution of ion exchange to the release of Al is negligible. In spite of the low pH the dissolution of Fe is negligible in all soil horizons. Small amounts of base cations are released by means of ion exchange and weathering of primary and secondary minerals. Ion exchange significantly (25%) contributes to the total acid neutralization in the topsoil, due to the relatively low contribution of other processes. The contribution of weathering of crystalline particles slowly rises during the progress of the experiments due to exhaustion of fast reacting compounds (NH 4 -oxalate extractable Al and adsorbed metal cations).