The growth responses of a grass, Poa pratensis, to elevated $CO_2$ and nitrogen were investigated. Light-saturated photosynthetic rate per unit leaf area increased with exposure to elevated $CO_2$, while dry weight did not respond to increased $CO_2$. Patterns of biomass allocation within plants, including leaf area, leaf area ratio, specific leaf area, and root to shoot ratios, were not altered by elevated $CO_2$, but changed considerably with N treatment. Shoot and whole-plant tissue N concentrations were significantly diluted by elevated $CO_2$ (Turkey test, p < 0.05). Total N content did not differ significantly among $CO_2$ treatments. The absence of a concomitant increase in N uptake under elevated $CO_2$may have caused a dilution in plant tissue (N), probably negating the positive effects of increased photosynthesis on biomass accumulation.