Large-scale forest conversion in Brazil, primarily to cattle pasture, contributes significantly to the global anthropogenic emission of CO₂ into the atmosphere. An alternative land-use, namely extractive reserves for forest residents, may serve as one means of using Amazonian forests sustainably and of maintaining carbon in living matter rather than adding it to that in the atmosphere.In the Seringal (former rubber estate) Porongaba (6,800 ha) of the Chico Mendes Extractive Reserve, Acre, Brazil, primary forest still covers more than 90% of the area. Total biomass in primary forest is estimated at 426 tons per ha, equivalent to 213 t C per ha. Rubber tappers effectively maintain about 60,000 tons of carbon per household (family unit) in forest biomass and thus out of the atmosphere. Deforestation of primary forest was less than 0.6% per yr — much less than rates of natural disturbances for other neotropical forests.Slash-and-burn agriculture in the Seringal Porongaba releases carbon at a gross rate of some 200 t C per yr per household. Net releases are much less, as regrowth forests absorb carbon at rates of about 9 t C per ha per yr. The net areal flux of carbon to the atmosphere from land-use in Seringal is much less than one ton of carbon per ha per yr, which is equivalent to less than 0.3% per yr of the carbon stock in forest biomass. If Seringal Porongaba is typical of the three million hectares in extractive reserves in Brazilian Amazonia, then these reserves are calculated to retain 0.6 Gigatons of carbon in the terrestrial biota.Adverse changes in income patterns for rubber tappers could lead to abandonment of extractive reserves or increased deforestation within them. Diversification and improvement of income from non-timber forest products are needed to maintain rubber tappers in extractive reserves. Most beneficiaries of carbon storage in these and other reserves live outside Brazil; devising means of recompensation for these benefits is a challenge for the global society.