Effects of elevated carbon dioxide (CO 2 ) and ozone (O 3 ) on wood properties of two initially 7-year-old silver birch (Betula pendula Roth) clones were studied after a fumigation during three growing seasons. Forty trees, representing two fast-growing clones (4 and 80), were exposed in open-top chambers to the following treatments: outside control, chamber control, 2 Â ambient [CO 2 ], 2 Â ambient [O 3 ] and 2 Â ambientAfter the 3-year exposure, the trees were felled and wood properties were analyzed. The treatments affected both stem wood structure and chemistry. Elevated [CO 2 ] increased annual ring width, and concentrations of extractives and starch, and decreased concentrations of cellulose and gravimetric lignin. Elevated O 3 decreased vessel percentage and increased cell wall percentage in clone 80. In vessel percentage, elevated CO 2 ameliorated the O 3 -induced decrease. In clone 4, elevated O 3 decreased nitrogen concentration of wood. The two clones had different wood properties. In clone 4, the concentrations of extractives, starch, soluble sugars and nitrogen were greater than in clone 80, while in clone 80 the concentrations of cellulose and acid-soluble lignin were higher. Clone 4 also had slightly longer fibres, greater vessel lumen diameter and vessel percentage than clone 80, while in clone 80 cell wall percentage was greater. Our results show that wood properties of young silver birch trees were altered under elevated CO 2 in both clones, whereas the effects of O 3 depended on clone.