Northern peatlands contain 1/3 of the world's soil carbon pool. Blanket bogs are peatlands that occur in maritime regions where precipitation is much greater than evapotranspiration. The role of blanket bogs in C dynamics has not been quantified. We describe an investigation of CO2 fluxes using an eddy covariance (EC) system in a pristine Atlantic blanket bog in Ireland during 2003 and 2004. This is the first multiyear study using EC techniques in a blanket bog. We found that the bog ecosystem was a CO2 sink for five months in each year. The annual CO2 flux had a sink magnitude of -49 (2003) and -61 g C m-2 (2004). These magnitudes are similar to boreal raised bogs, while higher values have been reported for boreal fens and lower for subarctic fens.