An investigation of the factors which effect the thermal shock resistance of polyphase ceramic systems was conducted with the model system zirconium carbide-graphite. The research was divided into two areas: (1) theoretical calculations of the individual material properties, which show that the included graphite particles may be regarded as spherical pores; and (2) experimental data, which substantiate the postulate that increased thermal shock resistance is a result of an increase in the ratio of strength over Young's modulus, brought about by the addition of the low Young's modulus phase. (Author).