Wheat was grown hydroponically for 23 days ( early boot stage) in a controlled environment at NO3- concentrations of 100 and 1000 μ,M and CO2 levels of 360 and 1200 μ,mol mo1-1. Nitrogen consumption and transpiration were measured daily. Tissue nitrogen concentration, total biomass, and percent root mass were measured at harvest. Nitrogen recovery and nitrogen use efficiency were calculated. Elevated CO2 increased nitrogen consumption of the 100 μ,M NO3- treatment by 13.6% and the 1000 μ,M NO3- treatment by 21.3%. These increases were particularly evident during tillering and early grain fill. Whole plant nitrogen, shoot NO3-, and root NO3- concentrations were increased by elevated CO2. High CO2increased biomass by 15% and increased percent root mass by 11 %. Nitrogen recovery and nitrogen use efficiency were similar at both CO2 concentrations. Transpiration (L m-2ground d-1) decreased by 40% in elevated CO2. The 1000 μ,M NO3- treatment consumed more NO3- than did the 100 μ,M NO3- treatment (8.1% in ambient CO2, 15.5% in elevated CO2); this effect was most pronounced during the last 5 days of the experiment (flag leaf emergence and early grain fill). Percent root mass increased as N concentration decreased from 1000 to 100 μ,M. Nitrogen levels did not significantly affect tissue N concentration or biomass. Nitrogen losses increased as N supply increased; an average of 16% of the nitrogen added to the 100 μ,M NO3- treatment was lost, while the 1000 μ,M NO3- treatment lost 21%. Nitrogen use efficiency and transpiration were similar in both nitrogen treatments.