Incoloy-800® fuel-cladding material has been corrosion-tested under heat-transfer conditions at metal temperatures up to 1410° F (766° C) in specially designed out-of-pile superheat facilities. The hydrogen and oxygen contents of the steam were controlled to simulate those found in boiling-water-reactor systems. The corrosion data from the 4000-h heat-transfer tests indicated good corrosion resistance up to at least 1300° F (704° C) metal temperature. A compositionally changed layer developed at the metal-oxide interface. The changed layer depth appeared to be a function of time and temperature of exposure. The descaled weight-loss data for the sheaths operated at a metal temperature of 1100 to 1300° F (593 to 704° C) indicate that greater than 80% of the oxide corrosion product adhered during the first 1000-h exposure, but only about 50% of the total oxidation product remained after 4000 h. The uniform corrosion experienced by the Incoloy-800® when exposed isothermally to 1050 and 1150° F (566 and 621° C) for 10 000h indicates an initially high-corrosion rate that decreases to a lower constant rate within the first 1000 h. An insignificant amount of the oxide was lost to the system.