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A recent study based on inventory data from the RAINFOR network, published in the journal Science, reported a relevant effect of an anomalous dry year (2005) on biomass accumulation and mortality in Amazon old-growth forests. Results were obtained by comparing inventory data taken before and after the dry year and point to biomass losses in consequence of drought. These losses were driven by large mortality increases at some plots and by small but diffuse declines in growth. If upscaled to the area affected by drought, the release of carbon (1.21 PgC) would be much larger than that resulting from deforestation in the area (0.3÷0.8 PgC) and would offset the carbon gained in the recent past (0.5 PgC). As the frequency of extreme dry years is expected to increase in future climate scenarios, regional carbon balances may be strongly impacted with a positive feedback on climate change. The main results of the paper are briefly presented and commented.