The elevated temperature (400 degrees C) erosion behaviour of six weld overlay coatings and wrought alloys of similar compositions, was analysed and the relative ranking of their erosion resistance has been developed. Microhardness tests performed on eroded samples showed that all materials experienced significant plastic deformation. No relationship was observed between hardness of the coatings at 400 degrees C and their erosion resistance. A new toughness parameter was developed based on the measured area under the microhardness profile curve, which represents the ability of a material to absorb impact energy. This parameter correlated well with erosion resistance for both weld overlays and wrought alloys. Also, for the wrought alloys, an increase in area under the true stress-strain curve or tensile toughness, corresponded to an increase in erosion resistance. The physical significance of the toughness parameter is discussed along with relationships between hardness, tensile properties and erosion resistance.