Particles of Soda Lime Silica Glass were used to simulate fly ash in the modelling of particle deposition from a high-temperature flue gas on to a superheater tube. The computational fluid dynamic code FLUENT was used and experimental deposition data were obtained from a rig comprising a small scale furnace containing an air-cooled probe. The effects of particle size, gas velocity and temperature on deposition were investigated. The effects of inertia, eddy impaction, thermophoresis and gravity on the particle trajectories were considered. The number of particles captured by the probe and the furnace surfaces were predicted and agreement with experimental results was found to be a function of particle size with the best agreement achieved for 16- and 26-mu m particles. Deposition was controlled by the kinetic energy of the particles and the adhesive forces of the surface. It is postulated that, for small particles, there was insufficient energy to bond them to the surface whereas for larger particles their kinetic energy was too targe. Thermophoresis did not play a significant part in the deposition process because, although the temperature gradient was large, 400 degrees C mm(-1) in the thermal boundary layer, the small particles (6 and 8 mu m) were unable to reach the thermal boundary layer (9 mm) which was much smaller than the hydrodynamic boundary layer (49.5 mm).