A b s t r a c t. The effect of intensive soil acidification on the genesis of Fe-, Al- and Mn-oxides and their relation to the soil aggregate stability were investigated in the Vienna Woods. Analyses were carried out on soil samples of 2.sites at 4 depths (0-5, 5-10, 10-20, and 20-30 cm) taken from the infiltration zone of the stem flow (S) of beech trees, which is strongly influenced by acid atmospheric depositions (soil-pH KC1 2.5 to 3.0), and from non-contaminated reference areas (R) between the trees, where the acid input is much lower (soil-pH KC1 5.5). The extreme soil acidification in the infiltration zone of stem flow led to intensive weathering of primary minerals, to neoformation and accumulation of crystallized, amorphous and organic-bound Fe-oxides, to lower concentrations of Al-and Mn-oxides and to a high increase in soil aggregate sta­bility, reflecting the aggregation effect of Fe-oxides, and the concomitant leaching of Mn and Al at a very low soil pH. Moreover, chemical extractions of the fine earth (water saturation extract and BaCI,-extraction) showed that Fe had accumulated in the strongly acidified soils also as water-soluble and exchangeable cation.