We propose a novel pragmatic approach of in situ 15 N and 13 C isotope labelling of trees for subsequent litter decomposition and turnover studies under field conditions. Using this method the labelling of even large trees under natural conditions is possible and compared to tree labelling under artificial conditions in greenhouses the in situ approach is less expensive. 13 C and 15 N labelling were carried out simultaneously via photosynthesis by tree gassing with 13 CO 2 and by stem injection of 15 NH 4 15 NO 3 . The aims of this study were: (i) to produce a sufficient quantity of labelled plant material for subsequent field incubation studies and (ii) to investigate the effectiveness and distribution of in situ 15 N ( 15 NH 4 15 NO 3 ) and 13 C ( 13 CO 2 ) labelling of Podocarpus falcatus, Croton macrostachys, Prunus africana and Cupressus lusitanica. The following targets need to be achieved: (i) Assuming almost natural litter fall conditions, enough labelled plant material must be produced in situ for the turnover experiment; (ii) intra-plant tracer enrichment shall be homogeneous; (iii) tracer enrichment should be comparable for different tree species; and (iv) tracer enrichment must be sufficient for subsequent litter turnover studies using the stable isotope approach. Our results clearly demonstrated that several kilograms of labelled plant material can be produced in situ. For many ecosystems, this amount is sufficient for a long term litter turnover experiment on a field scale under almost natural litter fall conditions. However, intra-plant label uptake of 13 C and 15 N was heterogeneous so that only leaves (litter) should be used for the turnover study. It could be shown that only a part of the labile C and N fraction in the leaves was labelled. Nevertheless, label uptake was sufficient for subsequent litter turnover studies.