A hard-sphere granular dynamics model of a two-dimensional gas-fluidised bed was experimentally validated using Positron Emission Particle Tracking (PEPT). In the model the Newtonian equations of motion are solved for each solid particle while taking into account the particle-particle and particle-wall collisions. The gas phase hydrodynamics is described by the spatially averaged Navier-Stokes,equations for two-phase flow. A quasi two-dimensional (i.e. narrow) bed of 0.185-m width and 0.4-m height with homogenous inflow conditions at 1.5 u(mf) was chosen as a test case. Glass particles (rho (p) = 2435 kg/m(3)) with diameters ranging from 1.25 to 1.5 mm were used as the bed material. The collision parameters required in the simulation were obtained from separate, independent measurements. In the PEPT experiment, the motion of a single tracer particle in the bed was tracked for 1 h. In the simulation, the motion of 15,000 particles was tracked for 45 s. The simulation data were time-averaged over 45 s for each particle and subsequently ensemble-averaged over all the particles in the simulation. The comparison was made on the basis of averaged velocity maps, "occupancy" plots and speed histograms. The results showed good agreement between experiment and simulation when the measured values for the collision parameters were used. When collisions were assumed to be fully elastic and perfectly smooth the agreement was much worse.