Branched iso- and anteiso-alkanes were conjointly used, with n-alkanes and PAHs, as specific molecular markers to trace environmental tobacco smoke (ETS) in particle-sized aerosols collected in the indoor and outdoor urban atmosphere. GC/MS and GC-FID were used for the determination of iso-, anteiso-, and n-alkanes and PAHs. The branched alkanes (ranging from C29 to C33) were detected only in particles in the accumulation range mode (<1.5 μm) in both indoor and outdoor samples. The concentrations of iso- and anteiso-alkanes in the indoor aerosols (0.758.53 ng/m3) were higher than those measured in outdoor samples (0.77-1.51 ng/m3). The indoor aerosol pattern of iso-, anteiso-, and their calculated diagnostic concentration ratios were characteristic for ETS. The compound distribution pattern of indoor n-alkanes (ranging from C21 to C33) was of biogenic origin, and the use of odd-to-even predominance running ratio curves indicated their cigarette smoke origin. The corresponding outdoor pattern and concentration ratios, although less characteristic than the indoor ones, also indicated ETS as the main source of these compounds. The distribution study of the branched alkanes between gas and particulate phase in indoor aerosol demonstrated their presence only in the particles. On the other hand, PAHs in the gas phase gave a compound pattern more characteristic of ETS components than the PAHs present in the particulate phase. Iso- and anteiso-alkanes, due to their specificity, their nonreactive character, their association with the accumulation range mode particles, and therefore, their long atmospheric residence time, are the most suitable tracers for particulate ETS emissions in the indoor and outdoor urban atmosphere.