Short-term in vitro assays are arising in order to determine the toxicity of native Diesel aerosol particles, due to its association with adverse health effects. Estimation of the real quantity and characteristics of the particles deposition on the cells cultures in these assays becomes necessary to establish correlations between the particle deposition conditions and the biological indicators of toxicity of the exposed cells. On that basis, it is the aim of this paper to analyze the deposition of sub-micron particles in an air/liquid interface cells exposure system by means of a CFD (computational fluid dynamics) code. Some comparisons with experimental and modelled results are shown to probe the validity of the method and a detailed analysis on the deposition of particles and efficiency of exposure-cells systems, with perpendicular contact, is carried out. Furthermore, a parametric study on the effect of particle diameter, particle density and flow inlet velocity revealed the importance of such parameters in the efficiency and pattern of particle deposition. (c) 2006 Elsevier Ltd. All rights reserved.