The continuing increase in atmospheric CO 2 concentration is predicted to enhance biomass production and to alter biochemical composition of plant tissues. In the present study, winter wheat ( Triticum aestivum L. cv. 'Batis') was grown under ambient air (BLOW, CO 2 concentration: 385 muL L (-1)) and free-air CO 2 enrichment (FACE, CO 2 concentration: 550 muL l (-1)) and two different nitrogen (N) fertilization levels (normal N supply: N100, 50% of normal N supply: N50). Mature kernels were milled into white flour and analyzed for the contents of crude protein, Osborne fractions, single gluten protein types and glutenin macropolymer. Elevated CO 2 caused significant reductions in crude protein and all protein fractions and types ( p < 0.001) except albumins and globulins. Effects were more pronounced in wheat samples supplied with normal amounts of N fertilizer. Crude protein was reduced by 14% (N100) and 9% (N50), gliadins by 20% and 13%, glutenins by 15% and 15% and glutenin macropolymer by 19% and 16%, respectively. Within gliadins, omega5-gliadins (-35/-22%) and omega1,2-gliadins (-27/-14%) were more affected than alpha-gliadins (-21/-13%) and gamma-gliadins (-16/-12%). Within glutenins, HMW subunits (-23/-18%) were more affected than LMW subunits (-12/-15%). According to these results, flour from high CO 2 grown grain will have a diminished baking quality. To our knowledge, these are the first results of elevated CO 2 concentrations impacts on wheat grain protein composition gained under relevant growing conditions at least for Central Europe.