THE brittleness of ceramic materials, compared with metals, limits their use in engineering, in spite of such attractive properties as high temperature strength and oxidation resistance. Possible solutions to the brittleness problem therefore continue to be of interest. One approach advocated1 for silicon nitride has been that of fibre reinforcement, practical feasibility of which has been demonstrated2. In the carbon/silica system Crivelli-Visconti3 and Cooper have shown that high work of fracture can be obtained : we present here mechanical property data for silicon nitride/silicon carbide fibre composite materials. The potential of silicon nitride ceramics as engineering materials has been described elsewhere4.