Discrete particle simulations of a segregating system are performed using various drag relations and boundary conditions, and compared to experiments. The boundary conditions on the walls are found to have a large influence on the segregation behaviour of the fluidised bed, where no-slip conditions result in unrealistic flow patterns. A polydispersity factor, which was recently derived on the basis of lattice-Boltzmann (LBM) simulations, is found to have a major effect on the segregation velocity and the final degree of segregation. The best agreement with experimental results is obtained with drag relations that were recently proposed based on LBM-simulations in combination with the aforementioned polydispersity factor. (c) 2006 Elsevier Ltd. All rights reserved.