This paper describes results of the work undertaken to estimate carbon release rates of biomass burning through the process of forest clearing in five test areas located in the Amazonian arc of deforestation. The experiments were carried out at the Caiabi Farm, near the town of Alta Floresta, state of Mato Grosso, Brazil, in five square areas of 1 ha each, denominated A, B, C, D, and E, with different characteristics of location and timing of fire. Test plot A was located in the frontier with a pasture, with three sides directly on the forest. Plot B was located inside the forest, with four edges directly on the forest. Plot C was located inside a deforested 9-hectare area. Plot D was located inside a deforested 4-hectare area. Plot E was located inside a deforested 4-hectare area. The vegetation in plots A, B, C, and E were cut and burned in the same year; in plot D the vegetation was cut in one year and burned 15 months later. Carbon emission rates for areas A and B, 22.7 % and 19.5 %, respectively, were found to be in the same range of values previously obtained in Manaus (state of Amazonas) and Tomé Açu (state of Pará). Carbon emission rates for areas C, D, and E were estimated as 47.5 %, 61.5 %, and 41.8 %, respectively. The effect of an extended curing could be clearly observed with the efficiency of area D. The effect of increasing the surrounding area of the test site could also be clearly observed with the efficiency of all the other test areas. The combustion efficiency, for areas cut and burned during the same year, tended to a value of nearly 50 % when plotted as a function of the total area burned. The biomass content of the test site was 496 t ha-1, and the amount of carbon on the ground before the burning was calculated as 138 t ha-1. Taking as an estimate that the biomass that remains unburned on the ground keeps the same average carbon content of fresh biomass, which is supported by the fact that the unburned material consists mainly of large logs, and considering the value of 50 % for the combustion efficiency, the amount of carbon released to the atmosphere as gases was calculated as 69 t ha-1. The amounts of CO2 and CO released to the atmosphere by the burning process were then estimated 228 t ha-1 and 15.9 t ha-1, respectively.