Two-dimensional channel flow of fluid laden with many particles is studied by direct numerical simulation using the Navier-Stokes equation coupled with the equation of motion for respective particles. Fractional four-step method with Crank-Nicolson scheme and ALE technique is adopted for P2P1 mixed finite element formulation of the governing equations for fluid motion. The motion and distribution of particles in the fluid is virtually described and the calculated relative viscosity is compared with previous results within the limits of possibility. The effect of the ratio of channel gap to particle diameter on the relative viscosity and the tubular pinch effect are also delineated. (c) 2005 Elsevier Ltd. All rights reserved.