The phenomena of particle-wall collisions including wall roughness and inter-particle collisions in a horizontal channel flow are analysed in detail by numerical calculations on the basis of the Lagrangian approach. In order to assess the effects of particle-wall collisions and inter-particle collisions independent on other phenomena, two-way coupling is neglected in this study. Integral values of the particle phase properties, such as mean velocities and fluctuating components averaged over the channel height are used to demonstrate the consequences of both transport effects. The ratios of the fluctuating components are deter-mined in order to assess the unisotropy of the particles fluctuating behaviour. Additionally, a channel with a larger height is considered in order to provide information on the scale-up of the effects observed in a narrow channel. For validating the Lagrangian models describing particle-wall and inter-particle collisions, numerical calculations for different particle size and mass loading are compared with measurements by phase-Doppler anemometry in the developed region of a channel with 35 mm height and 6 m length. The good agreement between measurements and calculations allow to conclude that the transport phenomena wall collisions and inter-particle collisions are modelled appropriately. (C) 2003 Published by Elsevier Science Ltd.