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Abstract The natural 15 N abundance (δ 15 N) of epiphytes and its N sources were studied in the canopy of a lowland rainforest in Costa Rica. Vascular and non-vascular epiphytes and canopy soils were collected from four canopy zones and analysed for N contents and δ 15 N signals. In addition, the N concentrations and δ 15 N signatures of bulk precipitation, throughfall and stemflow were measured during the wet and the dry season. The δ 15 N values of epiphyte leaves decreased significantly from the lower zones (means of -3·9 and -4·3‰) to the upper zones (means of -5·4 and -6·1‰) of the canopy. In contrast, δ 15 N signatures of canopy soils (average -0·3‰) differed little between the zones. Bulk deposition was enriched in 15 N (+4·3‰) compared to all other potential N sources and was higher than throughfall and stemflow (+0·5 to -1·3‰). δ 15 N values of atmospheric deposition were inversely related to those of the epiphyte leaves, whereas N isotopic composition of canopy soils did not vary significantly. Consequently, it is concluded that the variations in foliar N isotope composition of epiphytes were not simply caused by utilization of isotopically different N sources, but by different 15 N discrimination during N acquisition. [ABSTRACT FROM AUTHOR]