Measurements of net ecosystem exchange (NEE) of CO2 were made via the eddy covariance technique over a boreal treeline woodland near Churchill, Manitoba, Canada during the growing season of 1997. Precipitation and temperature deviated only slightly from long-term normals and energy balance measurements were similar to those in other years. The mean daily Bowen ratio was 1.16¿0.12 (S.E.) and mean daily evaporation was 1.8¿0.19 (S.E.) mm. Mean daily energy balance closure was 0.92¿0.036 (S.E.). A curvilinear relationship was used to model the relationship between half-hourly NEE and photosynthetically active radiation, yielding r2 of 0.51. Poor relationships were found between nighttime ecosystem respiration and air and soil temperatures. The best fit was found for in-canopy air temperature using average nighttime data (r2=0.20). Daily NEE showed a seasonal trend with the peak uptake (6.2 g CO2 m-2 d-1) occurring in late July. The mean daily NEE was an uptake of 1.7 g CO2 m-2 d-1. Accumulated NEE estimated for the 90-day measurement period was between 86 and 151 g CO2 m-2. CO2 fluxes were found to be considerably smaller than for central and southern boreal forest sites and only slightly larger than tundra sites. ¿ 1999 American Geophysical Union