Fluxes of CO2, water vapour and sensible heal above a forest in the Campine region in Belgium are being measured employing eddy covariance technique since early 1996. On a clear day, the CO2 flux showed a midday peak and a subsequent decline. During mid July, the daily net ecosystem CO2 exchange (NEE) was high and negative (implying the ecosystem was actively accumulating carbon). After mid October, NEE was positive, suggesting that the ecosystem was a source of CO2 to the atmosphere. Over a period of 100 days, the ecosystem accumulated about 13 mol m(-2) of CO2.