The study of natural isotopic abundance signatures is useful to gain further insights in the processes resulting in depthwise changes in the composition of soil organic matter (SOM). Objectives were to describe the 6I3C and 6I5N abundances of SOM with depth in soils from a 153-year old beech (Bl), a 119-year old spruce (Fl) and a 61-year old spruce (F2) stand at Solling, north-west Germany, and to study, how podzolisation affects the isotopic abundances of I3C and I5N in the SOM. The degree of podzolisation decreased in the order F1> B1 > F2. At the surface of the humus layer of all three sites, 6I3C values are approximately 1 to 4OmO higher than in the leaves and needles, probably mainly due to the discrimination of I3C by microbial decomposition. I3C abundances in the organic layers of B1 and F2 increased only slightly from -27.6OmO PDB (Bl, L) to -27.2OmO PDB (Bl, Oh) and from -26.3% PDB (F2, L) to -25.9% PDB (F2, Oh), suggesting that biotic activity resulted in mixing of organic matter. At F1, however, I3C abundance increased from -27.5%0 PDB (L) to -26.0?? PDB (Oh) which reflects the lack of mixing by animals. In the upper 2-4cm of the mineral soil, i.e., in the eluvial horizons Aeh, I3C values showed a minimum at the spruce sites which was presumably related to translocation of I3C enriched fulvic acids. Depthwise changes in 6″N values were not related to podzolisation processes. At all three sites, a N enrichment with depth occurred in the mineral soil which is the result of the discrimination of I5N by microbial decomposition.