Four- to seven-year-old spruce trees (Picea abies) were exposed to three CO2 concentrations (280, 420 and 560 cm3 m−3) and three rates of wet N deposition (0, 30 and 90 kg ha−1 year−1) for 3 years in a simulated montane forest climate. Six trees from each of six clones were grown in competition in each of nine 100 × 70 × 36 cm model ecosystems with nutrient-poor natural forest soil. Stem dises were analysed using X-ray densitometry. The radial stem increment was not affected by [CO2] but increased with increasing rates of N deposition. Wood density was increased by [CO2], but decreased by N deposition. Wood-starch concentration increased, and wood nitrogen concentration decreased with increasing [CO2], but neither was affected by N deposition. The lignin concentration in wood was affected by neither [CO2] nor N deposition. Our results suggest that, under natural growth conditions, rising atmospheric [CO2] will not lead to enhanced radial stem growth of spruce, but atmospheric N deposition will, and in some regions is probably already doing so. Elevated [CO2], however, will lead to denser wood unless this effect is compensated by massive atmospheric N deposition. If can be speculated that greater wood density under elevated [CO2] may alter the mechanical properties of wood, and higher ratios of C/N and lignin/N in wood grown at elevated [CO2] may affect nutrient cycles of forest ecosystems.