Sagebrush-steppe ecosystems cover more than 36 million ha in North America and represent an important economic and environmental resource. Because cold periods during the fall, winter, and early spring comprise a significant part of the year for sagebrush-steppe ecosystems, it is critical to determine losses of CO₂ during these cold periods. We used Bowen ratio/energy balance techniques to measure CO₂ exchange during the fall, winter, and early spring periods on a representative sagebrush-steppe site near Dubois, Idaho and another site near Burns, Oregon during 2000-01. Mean values of CO₂ loss for the cold period were 1.37 ± 0.79 g CO₂ m^-2 d^-1 for the Dubois site and 0.61 ± 0.58 g CO₂ m^-2 d^-1 for the less-productive site near Burns. As a result, 644 g CO₂ m^-2 were lost to the atmosphere at the Dubois site and 273 g CO₂ m^-2 were lost at the Burns site during the period when net daily CO₂ exchange remained negative (late-fall, winter, and early spring). Multivariate analysis of these data showed that CO₂ fluxes during the cold period were most closely associated with soil temperature, wind speed, and depth of snow cover.