A program was undertaken by The Detroit Edison Company to determine the rate of corrosion and the relative corrosion resistance in an unstressed condition of various materials that could be used in the construction of steam generators, piping, and turbines. Specimens were exposed in a steam atmosphere at 380 psi and at temperatures of 925 F and 1100 F. The investigation required 5 years for completion; during that time 46 different materials were studied, including nickel, nickel-copper alloys, chromium and chromium-nickel stainless steels, medium- and low-alloy steels, carbon steels, and alloy cast iron. The tests were conducted under plant-operating conditions, and samples were exposed in superheated station steam for periods ranging from 4000 to 16,000 hr. Weight-loss, hardness, and metallographic data were obtained after successive exposure periods for many of the samples. Trends in the corrosion rate were plotted for some of the materials. The test results, reported in this paper, indicate that the weight loss of plain-carbon steel exposed to 1100 F steam continues at a high rate, whereas the rate of loss of the alloyed materials decreases with time. The high chromium-nickel and the 12-chromium stainless steels were the most corrosion-resistant. The corrosion rate of 0.50 molybdenum and 1.0 chromium steels compared favorably with that of steels containing 5 chromium. Nonferrous materials were not as corrosion-resistant in high-temperature steam as the high-alloy ferrous materials. Materials which corroded rapidly at 1100 F corroded only slightly at 925 F, and at this lower temperature there was little difference between the rate of corrosion of plain carbon and alloy steels.