Tunable diode laser trace gas analyzers have been used for many years to measure trace gas fluxes using techniques such as mass balance, gradient, and eddy covariance. Recently they have been used to measure the carbon isotope ratio in respired carbon dioxide using Keeling plots. Later work extended their use to flux gradient measurements and carbon dioxide oxygen isotope measurements. In all of these applications the analyzer was calibrated often to achieve the accuracy required for isotope ratio measurements and the flow rate was kept low to minimize the consumption of calibration gases. The low flow rate also reduced potential errors due to mismatched flow or pressure between air samples and calibration gases. The eddy covariance technique has the potential to give a more direct measurement of isotopic carbon dioxide fluxes, but it requires high frequency response, which can only be achieved at higher flow rates. High flow rates require a carefully designed sampling system to avoid excessive consumption of calibration gases and to avoid any bias between the air sample and calibration gas measurements. Results of laboratory and field experiments will be given to evaluate the feasibility of using a tunable diode laser trace gas analyzer for eddy covariance measurements of isotopic carbon dioxide fluxes.