BIOMASS burning is a primary source of many trace substances that are important in atmospheric chemistry. More than 80% of the world's biomass burning takes place in the tropics as a result of savanna fires, forest-clearing activity, and the burning of agricultural waste and wood. Here we report results from laboratory studies on the emission of nitrogen-containing compounds from the burning of dry vegetation. We find that the emission rates of NOX, HCN and CH3CN are sufficient to contribute significantly to the global atmospheric budget of the compounds. Furthermore, possibly up to half of the biomass nitrogen can be converted to molecular nitrogen, N2, leading to an estimated annual loss of 12?28 x 1012g of biomass nitrogen ('pyrodenitrification'), equal to ~9-20% of the estimated global rate of terrestrial nitrogen fixation.