We used two independent approaches, biometry and micrometeorology, to determine the net ecosystem production (NEP) of an old growth forest in Para, Brazil. Biometric inventories indicated that the forest was either a source or, at most, a modest sink of carbon from 1984 to 2000 (+0.8 +/- 2 Mg C(.)ha(-1.)yr(-1); a positive flux indicates carbon loss by the forest, a negative flux indicates carbon gain). Eddy covariance measurements of CO2 exchange were made from July...