Symmetrical wedge models of sharp leading edges were fabricated from candidate refractory materials and tested in a 10-Mw-arc-heated, freejet facility producing nominal plenum conditions of 380 psia and 5500 °F. Experiments were first conducted with specially developed temperature probes to determine heat-transfer coefficients and recovery temperature at various stations in the freejet. Tests of the models were then carried out at appropriate stations in the freejet to produce tip temperatures in the range 3200-3900°F to simulate temperatures such as would be encountered in flight at velocities up to 7800 fps at altitudes near 70,000 ft. Successful performance was obtained with several models having 0.03-in. or smaller radii with little or no erosion occurring during runs of 13 sec duration. The best results were obtained with solid models of a ductile metallic alloy of hafnium-20% tantalum and with coatings of this alloy on a graphite or tantalum-10% tungsten alloy substrate. Several brittle materials, such as metallic carbides and boron nitride, showed good erosion resistance, but fracture was frequently encountered due to the unusually severe thermal shock associated with the test. The results indicate that the materials may be serviceable at similar velocities and altitudes near sea level.