There is a need to develop new materials for heat exchangers in power plants that can operate at higher temperatures. These must have acceptable properties, including corrosion and erosion-corrosion resistance, under operating conditions. The current research involves an investigation into the erosion-corrosion performance of ferritic and austenitic steels in a fluidized-bed rig at temperatures of 400degreesC to 700degreesC and impact speeds up to 9 m s(-1), with aims of defining parameters that-can lead to unacceptable rates of material loss and to generate data that can be incorporated into lifetime prediction models. Some preliminary results from the programme are presented in this paper. Alloy P91 has been exposed under fluidized-bed erosion-corrosion conditions at 550 T, at impact angles of 30degrees and 90degrees. The impacting particles were sand, average diameter of 175 gm. Under these conditions, the specimens did not exhibit any overall thickness losses; indeed, in all cases, overall increases in thickness were observed, consistent with erosion-enhanced oxidation being the dominant degradation process. These increases were dependent on impact angle and impact speed, but, for both angles, a maximum value was observed at speeds above about 8 m s(-1). Ongoing research is investigating the modes of degradation under these erosion- corrosion conditions.