Substrate hardness is sometimes used as a guide to the wear resistance of alloys. However, it been documented that there is often much less correlation between particle erosion resistance and hardness. This has been attributed to the high strain rates of erosion impacts compared with those involved in a static hardness test. Under erosion-corrosion conditions, where formation of oxide scales in a gaseous environment can influence markedly the extents of material damage, material hardness may influence the interactions of oxidation and impact damage. The present study has investigated this phenomenon. It has involved testing, in a fluidized-bed erosion-corrosion rig, a range of materials of various hardnesses, including mild steel, 310 stainless steel, a duplex 22% Cr-8% Ni-3% Mo alloy (under two heat-treatment conditions) and two cobalt-based alloys, Ultimet and Castolin 906. The alloys were exposed at temperatures up to 560-degrees-C and at a velocity of 5.8 m s-1 in a fluidized-bed containing 100 mum alumina erodent particles. This paper is concerned primarily with the general trends of erosion resistance as a function of material hardness under erosion-dominated, erosion-corrosion-dominated and corrosion-dominated conditions. At relatively low temperatures, where erosion dominates, there is no obvious correlation between the two parameters. However, at higher temperatures where oxidation plays a more significant role, the rate of erosion generally increases with increasing substrate hardness. Possible reasons for these observations are proposed and discussed in relation to earlier results from the literature.