Although increasing tropospheric ozone (O₃) concentrations as well as precursor NO₂ emissions and N deposition have been observed, the combination of their effects on deciduous trees is little understood. We therefore examined the growth and leaf injury response of a model tree (Populus ×euramericana (Dode) Guinier cuttings exposed before flush and until they reached a height of more than 1 m) to low and high soil N supply (105 or 315 mg N·L⁻¹ substrate volume), to filtered air, and to filtered air with NO₂ (sinusoidal daily course with a mean of 100 nL·L⁻¹), with O₃ (60 nL·L⁻¹), or with a combination of both in climate-controlled chambers. High soil N increased total plant dry weight, leaf area, and xylem radius in plants fumigated with or without added NO₂ or O₃. The number of leaves increased with high soil N independent of added NO₂. The stomatal density was influenced by soil N and by fumigations, but the appearance of leaf injury symptoms, leaf loss, specific leaf weight, and bark radius were not modified by the soil N regimes. NO₂ alone, though applied in a sixfold ambient concentration, did not significantly increase plant growth. NO₂ and O₃ alone had opposite effects on specific leaf dry weight, stomatal density, and in the high fertilization regime, on the bark radius. The decrease in specific leaf dry weight and the appearance of early leaf symptoms were enhanced by NO₂ added to O₃. Visible leaf injury caused by O₃ increased in parallel with microscopic changes in mesophyll cell walls, in the starch and protein patterns of mesophyll cells, in the bark cell content, and in the phloem sieve pores. NO₂ enhanced the negative effect of O₃ rather than compensated for a low soil N supply.