As part of the Large-Scale Biosphere-Atmosphere Experiment in Amazonia (LBA), PM10 aerosol was collected during both the wet and dry (biomass burning) seasons of 1999 and analyzed for total water-soluble organic nitrogen (WSON), urea, and 17 amino acids. In addition to total WSON the inorganic N species nitrate (NO3-), nitrite (NO2-), and ammonium (NH4+) were also analyzed. WSON was found to represent ~45% (mean concentration ~3.5 nmol N/m3) and ~43% (mean concentration ~61 nmol N/m3) of the total N in wet and dry season aerosol samples, respectively. Urea and amino N made up ~19% of the total organic N in dry season aerosols and ~2.5% of the total organic N in wet season aerosols; the majority of WSON, ~80% in the dry season and ~97% in the wet season, remained uncharacterized. The results suggest that biomass burning is a source of WSON, yet poorly understood (since this data set represents the first study of WSON in the context of biomass burning). Future studies aimed at determining the magnitude of WSON released from biomass burning globally, its species composition, and its biogeochemical significance are needed.