Abstract A biochemical model of leaf photosynthesis, in conjunction with a stomatal conductance model, was applied to C 4 tallgrass species ( Andropogon gerardii, Sorghastrum nutans, Panicum virgatum) in northeastern Kansas, USA. The modeled photosynthetic rates of individual leaves were scaled up to the canopy level using a simple canopy radiative transfer model. Comparisons with field measurements, using the micrometeorological eddy correlation technique, showed that the model simulated the magnitudes and the diurnal variations of canopy photosynthesis adequately under well-watered conditions. Although the model overestimated measured canopy photosynthesis by 4–7 μmol m −2 s −1 under moisture stress conditions (where 1 μmol m −2 s −1 ≈ 0.044 mg m −2 s −1), it did seem to simulate the diurnal patterns (e.g. morning peak) realistically. Using similar scaling-up procedures, values of canopy stomatal conductance were also computed from the model. The modeled canopy stomatal conductance agreed with measured values reasonably well (within 0.2 mol m −2 s −1, where 1 mol m −2 s −1 ≈ 0.0249 m s −1 when P = 100 kPa and T = 300°K, under well-watered conditions and within 0.05 mol m −2 s −1 under moisture stress conditions).