Winter wheat plants were grown under controlled atmospheric and light conditions for 25 days to assess the response of photosynthesis, respiration and carbon allocation to elevated ambient CO2 concentration. Daily balance of carbon fixation and loss was measured separately for shoots and roots including root exudation. Doubled CO2 (700 mumol CO2 mol-1) stimulated photosynthetic CO2 uptake and dark respiration rate when calculated on the leaf area basis. However, total daily carbon gain per plant and total dry matter of shoot was lower for high-CO2-grown plants due to reduced leaf area. After 23 days of exposition to high CO2, photosynthesis was depressed probably due to limiting regeneration of ribulose bisphosphate. Both stomatal resistance and water use efficiency were markedly higher in high-CO2-grown plants. Higher evaporative demand in low-CO2-grown plants promoted root elongation. Total root length was 160% of that in high-CO2-grown plants. Root exudation of high-CO2-grown plants was higher in the first days of plant development, but the inhibition of net photosynthesis was followed by a decrease in exudation.