Changes in forest structure were examined 10-15 months after an unprecedented understorey wildfire burnt previously undisturbed primary forest in central Brazilian Amazonia, following the severe 1997-1998 El Niño dry season. On the basis of 20 0.25 ha plots (10 m x 250 m) in both burnt and unburnt forest, we found marked differences in the overall live biomass, canopy openness and understorey vegetation. On average, 36% of all trees equal to or greater than 10 cm DBH were found to be dead in the burnt forest, and there was also a near-complete mortality in all pre-burn saplings. Using an allometric equation to predict biomass mortality we estimate that the tree mortality rates found would commit an additional 25.5 t C/ha to be released from these BFs. The dramatic increase of aboveground dead biomass in BF is of major global concern because of the increased flux of CO2 to the atmosphere, which has a role in enhancing the greenhouse effect and promoting climate change.