The effectiveness of fugitive interfacial carbon coatings in Nextel(TM) 720-based composites was investigated. Dense (>90%) matrix (calcium aluminosilicate, 0 degrees and +/- 45 degrees) composites and porous matrix (mullite/alumina, eight-harness satin fabric) composites were fabricated and tensile tested in two control conditions (uncoated or carbon-coated) and with the carbon removed (fugitive interface). Results indicated that carbon removal in dense matrix composites did not significantly change unidirectional composite strength, even after long-term exposure at 1000 degrees C. For porous matrix composites, composite strength was independent of the fiber/matrix inter face, even after exposure at 1150 degrees C for 500 h in air.