Sagebrush-steppe ecosystems cover expansive areas in western North America and likely make important contributions to the global carbon cycle. However, few studies have measured CO₂ fluxes in these important ecosystems. The objective of our study was to determine CO₂ fluxes in a representative sagebrush-steppe ecosystem at the U.S. Sheep Experiment Station near Dubois, Idaho. The Bowen ratio/energy balance technique was used to continuously measure net CO₂ fluxes above the ungrazed, sagebrush-steppe site during the growing seasons of 1996-2001. Daily net CO₂ uptake was highest during June and, depending on the year, total fluxes for the growing season ranged from +284 to +1,103 g CO₂ m^-2. Based on flux measurements obtained during the late fall, winter, and early spring of 2000-01, we used a mean daily flux of -1.37 g CO₂ m^-2 d^-1 during the cold period to estimate annual CO₂ fluxes. These annual values suggest that sagebrush-steppe ecosystems are sinks for CO₂ during some years and sources during other years, depending on the environmental conditions for the particular year.