Thermophoresis of ultrafine particles in a turbulent pipe flow was studied using high-temperature and high-concentration polydisperse ultrafine particles. Experimental conditions were designed to simulate particle behaviour in an automobile exhaust pipe, with a particular focus on establishing similar particle residence time. From the experimental results, thermophoresis was found to be a dominant mechanism for ultrafine particle deposition in the turbulent pipe flow. A previous thermophoretic deposition model was found to be inadequate with respect to estimating the results of the experimental conditions. In this study, the experimental data and the computational analysis results reflect the necessity of establishing a new formula for thermophoretic deposition for high-concentration polydisperse ultrafine particles in a pipe flow. (c) 2006 Elsevier Ltd. All rights reserved.