Indications are emerging that N cycling differs between pristine and more disturbed or polluted forest ecosystems. In 100 pristine old-growth forest catchments of South Chile, having a low N deposition, N losses between 0.2 and 3.5 kg N ha-1 yr-1 were observed. The DON and DIN drained from these catchments was 20 and 80%, respectively (Perakis & Hedin, 2002). Rainfall was the main factor affecting the DON:DIN los ratio. The contribution of DON to N losses from rorests of more polluted regions of the world, on the ogher hand, is negligible. MacDonald ete al., (2002) showed that in forests of Europe (N deposition 1-60 kg Nha-1 yr-1)the predominant N loss mechanism was NO3 leaching (1-40 kg N ha-1 yr-1). Nitrate formation in N polluted forests seemed to be largely controlled by N input and N enrichment of the forest floor. Organic layer C:N ratios of ca. 25 seem to be crucial to initiate more intense nitrification and subsequent NO3 or losses. It has been suggested that forest soils may possess a substantial biotic or abiotic NO3 NH4+ retention mechanism controlling DON and DIN losses. The exact mechanisms, the capacity and time frame of these alternative N retention processes in forest solis are still unclear. Here we present an initial study comparing N turnover in a pristine and a more polluted forest.FONDECYT624FONDECYT