The mechanical properties of silicon carbide (SiC) and sapphire filaments pertinent to the initial design of a metal matrix composite have been documented. The strength contributions of these filaments to a composite were simulated with tensile tests of self-abraded samples. The strength of virgin SiC filament was found to decrease linearly to about 1100 C (2012 F) and exponentially above this temperature. The abraded strength was found to be constant, as a function of temperature, to about 1100 C (2112 F). The loss of high temperature strength was correlated with the reaction between SiC and the fiber's W core. The strength of single crystal sapphire as a function of temperature was determined for both a-and c-axis filaments. Similar tests were conducted on ruby fiber. Ruby fiber was found to be significantly stronger than pure sapphire and insensitive to abrasion above 500 C (932 F). The strength of ruby fiber as a function of chronic ion content showed that the optimum dopant level has not yet been reached.