Fine particle (PM2.5) samples were collected, using a charcoal diffusion denuder, in two urban areas of Chile, Santiago and Temuco, during the winter and spring season of 1998. Molecular markers of the organic aerosol were determined using GC/MS. Diagnostic ratios and molecular tracers were used to investigate the origin of carbonaceous aerosols. As main sources, road and non-road engine emissions in Santiago, and wood burning in Temuco were identified. Cluster analysis was used to compare the chemical characteristics of carbonaceous aerosols between the two urban environments. Distinct differences between Santiago and Temuco samples were observed. High concentrations of isoprenoid (30-69ngm-3) and unresolved complex mixture (UCM) of hydrocarbons (839-1369ngm-3) were found in Santiago. High concentrations of polynuclear aromatic hydrocarbons (751±304ngm-3) and their oxygenated derivatives (4±2ngm-3), and of n-alk-1-enes (16±13ngm-3) were observed in Temuco. © 2002 Elsevier Science Ltd. All rights reserved.