This study aims to investigate the changes in isotope ratios in foliage and soils of two Norway spruce (Picea abies [L.] Karst.) forests greatly differing in their atmospheric N deposition and climatic conditions. As expected, both N concentrations and δ¹⁵N values in needles and roots were found to be significantly higher in the Solling stand (N-saturated) compared to the Hyytialä stand (N-poor). For both stands a typical vertical gradient of the soil ¹⁵N-enrichment was observed. As expected, the soil of N-polluted site (Solling) was ¹⁵N-enriched significantly more than that of N-limited site (Hyytialä) and this is explained by the presence of marked NO₃^– leaching at the Solling site. Although the annual trends (1990–1994) of N concentration in the foliage of spruce trees remained almost constant, their δ¹⁵N values significantly decreased with the increasing years of sampling. The ¹⁵N-depletion in spruce needle litter from 1990 to 1995 was by 2.0‰. This is explained by a slight decrease in N deposition at Solling site during this period.