The performance of six thoracic sampler types has been assessed against the CEN/ISO thoracic convention. Samplers tested included the CATHIA thoracic sampler, a modified form of the SIMPEDS cyclone, the IOM thoracic sampler, the GK2.69 thoracic cyclone, a modified IOM inhalable sampler with a foam plug insert and a modified cowled sampler of the type usually used for sampling fibres. Penetration measurements were carried out using an aerodynamic particle sizer-based system with an effective operating range extending up to 20 mu m. Results of measurements on isolated samplers under calm air conditions showed the GK2.69 and modified SIMPEDS cyclones to agree well with the thoracic convention. Measurements on internal separation efficiency indicated that both the IOM thoracic sampler and modified IOM inhalable sampler would operate close to the convention at wind speeds between 0.5 and 4 m s(-1). Penetration measurements on the CATHIA sampler showed it to oversample with respect to the thoracic convention, although there were small discrepancies between data from this study and measurements made elsewhere. The modified cowled sampler measurements indicated that there would be significant bias with respect to the thoracic convention for some lognormal aerosol distributions. However, the modification was exceptionally cost effective, and may be worth developing further. Crown